* Rename StringXxx to StrXxx in string_util.h and its users

This makes the naming consistent within string_util and moves is the
Abseil convention.

* Style guide is 2 spaces before end of line "//" comments

* Rename StrPrintF/StringPrintF to StrFormat for absl compatibility.

On Windows the Shlwapi.h file has a macro:

  #define StrCat lstrcatA

And benchmark/src/string_util.h defines StrCat and it is renamed to
lstrcatA if we don't undef the macro in Shlwapi.h. This is an innocuous
bug if string_util.h is included after Shlwapi.h, but it is a compile
error if string_util.h is included before Shlwapi.h.

This fixes issue #545.

Upstream spelling fix changes from Pony, ec47ba8f565726414552f4bbf97d7,
by ka7@la-evento.com that effected google/benchmark.

* Add Solaris support

Define BENCHMARK_OS_SOLARIS for Solaris.

Platform specific implementations added:
* number of CPUs detection
* CPU cycles per second detection
* Thread CPU usage
* Process CPU usage

* Remove the special case for per process CPU time for Solaris, it's the same as the default.

* Print the executable name as part of the context.

A common use case of the library is to run two different
versions of a benchmark to compare them. In my experience
this often means compiling a benchmark twice, renaming
one of the executables, and then running the executables
back-to-back. In this case the name of the executable
is important contextually information.  Unfortunately the
benchmark does not report this information.

This patch adds the executable name to the context reported
by the benchmark.

* attempt to fix tests on Windows

* attempt to fix tests on Windows

Due to ADL lookup performed on the begin and end functions
of `for (auto _ : State)`, std::iterator_traits may get
incidentally instantiated. This patch ensures the library
can tolerate that.

* Don't include <sys/resource.h> on Fuchsia.

It doesn't support POSIX resource measurement and timing APIs.

Change-Id: Ifab4bac4296575f042c699db1ce5a4f7c2d82893

* Add BENCHMARK_OS_FUCHSIA for Fuchsia

Change-Id: Ic536f9625e413270285fbfd08471dcb6753ddad1

* Improve State packing: put important members on first cache line.

This patch does a few different things to ensure commonly accessed
data is on the first cache line of the `State` object.

First, it moves the `error_occurred_` member to reside after
the `started_` and `finished_` bools, since there was internal
padding there that was unused.

Second, it moves `batch_leftover_` and `max_iterations` further up
in the struct declaration. These variables are used in the calculation
of `iterations()` which users might call within the loop. Therefore
it's more important they exist on the first cache line.

Finally, this patch turns the bool members into bitfields. Although
this shouldn't have much of an effect currently, because padding is
still needed between the last bool and the first size_t, it should
help in future changes that require more "bool like" members.

* Remove bitfield change for now

* Move bools (and their padding) to end of "first cache line" vars.

I think it makes the most sense to move the padding required
following the group of bools to the end of the variables we want
on the first cache line.

This also means that the `total_iterations_` variable, which is the
most accessed, has the same address as the State object.

* Fix static assertion after moving bools

* Support State::KeepRunningBatch().

State::KeepRunning() can take large amounts of time relative to quick
operations (on the order of 1ns, depending on hardware). For such
sensitive operations, it is recommended to run batches of repeated
operations.

This commit simplifies handling of total_iterations_. Rather than
predecrementing such that total_iterations_ == 1 signals that
KeepRunning() should exit, total_iterations_ == 0 now signals the
intention for the benchmark to exit.

* Create better fast path in State::KeepRunningBatch()

* Replace int parameter with size_t to fix signed mismatch warnings

* Ensure benchmark State has been started even on error.

* Simplify KeepRunningBatch()

* Implement KeepRunning() in terms of KeepRunningBatch().

* Improve codegen by helping the compiler undestand dead code.

* Dummy commit for build bots' benefit.

* Attempt to fix travis timeouts during apt-get.

During some builds, travis fails to update the apt-get indexes.
This causes the build to fail in different ways.

This patch attempts to avoid this issue by manually calling
apt-get update. I'm not sure if it'll work, but it's worth a try.

* Fix missing semicolons in command

The appveyor bot sometimes fails because the time it
outputs is 6 digits long, but the output test regex expects at most
5 digits. This patch increases the size to 6 digits to placate the
test. This should not *really* affect the correctness of the test.

We're propagating extra warning flags to the gtest build, which
can cause it to fail. This patch prevents passing "-Wextra" to
gtest, since the library itself doesn't test with that flag.

* Support State::KeepRunningBatch().

State::KeepRunning() can take large amounts of time relative to quick
operations (on the order of 1ns, depending on hardware). For such
sensitive operations, it is recommended to run batches of repeated
operations.

This commit simplifies handling of total_iterations_. Rather than
predecrementing such that total_iterations_ == 1 signals that
KeepRunning() should exit, total_iterations_ == 0 now signals the
intention for the benchmark to exit.

* Create better fast path in State::KeepRunningBatch()

* Replace int parameter with size_t to fix signed mismatch warnings

* Ensure benchmark State has been started even on error.

* Simplify KeepRunningBatch()

conversion in sysinfo.cc

Some command line or build systems may already set these (eg, bazel) so
make sure that takes priority.

Fixes #513

Prevent GTest and GMock from being installed with Google Benchmark.

When users satisfy the GTest dependancy by placing a googletest
directory in the project, the targets from GTest and GMock incorrectly
get installed along side this library. We shouldn't be installing
our test dependancies.

This patch forces the options that control installation for googletest
to OFF.

For people who get this library via CMake's AddExternalProject like me.
Would like a long term tutorial from someone who really understands CMake on how to actually link an externalproject's dependencies to another added external project.

* Add support for GTest based unit tests.

As Dominic and I have previously discussed, there is some
need/desire to improve the testing situation in Google Benchmark.

One step to fixing this problem is to make it easier to write
unit tests by adding support for GTest, which is what this patch does.

By default it looks for an installed version of GTest. However the
user can specify -DBENCHMARK_BUILD_EXTERNAL_GTEST=ON to instead
download, build, and use copy of gtest from source. This is
quite useful when Benchmark is being built in non-standard configurations,
such as against libc++ or in 32 bit mode.

This patch documents the newly added v2 branch, which will
be used to stage, test, and receive feedback on upcoming
features, most of which will be breaking changes which can't
be directly applied to master.

* CMake: implement LTO for clang. Fixes #478

* LTO: add basic docs about required executables.

* Initial CLA Requirement

* Added Installation steps to the Readme.md

* Fixed error in running benchmark of Installation

* Remove unwanted commands

Removed the lengthy install procedure with suggested install mechanism

Old output example:
```
Benchmark                                                 Time           CPU Iterations  CPUTime,s   Pixels/s ThreadingFactor
------------------------------------------------------------------------------------------------------------------------------
20170525_0036TEST.RAF/threads:8/real_time                45 ms         45 ms         16   0.718738 79.6277M/s   0.999978   2.41419GB/s    22.2613 items/s FileSize,MB=111.050781; MPix=57.231360
```

New output example:
```
Benchmark                                                 Time           CPU Iterations  CPUTime,s   Pixels/s ThreadingFactor
------------------------------------------------------------------------------------------------------------------------------
20170525_0036TEST.RAF/threads:8/real_time                45 ms         45 ms         16   0.713575 80.1713M/s        0.999571   2.43067GB/s    22.4133 items/s FileSize,MB=111.050781; MPix=57.231360
```

This patch primarily changes the BENCHMARK_UNREACHABLE()
implementation under MSVC to use __assume(false) instead
of being a NORETURN function, which ironically caused
unreachable code warnings.

Second, since the NOTHROW function attempt generated the
warnings we meant to avoid, it has been replaced with a dummy
null statement.

* Improve CPU Cache info reporting -- Add Windows support.

This patch does a couple of thing regarding CPU Cache reporting.

First, it adds an implementation on Windows. Second it fixes
the JSONReporter to correctly (and actually) output the CPU
configuration information.

And finally, third, it detects and reports the number of
physical CPU's that share the same cache.

* Refactor System information collection.

This patch refactors the system information collection,
and in particular information about the target CPU. The
motivation is to make it easier to access CPU information,
and easier to add new information as need be.

This patch additionally adds information about the cache
sizes of the CPU.

* Address review comments: Clean up integer types.

This commit cleans up the integer types used in ValueUnion to
follow the Google style guide.

Additionally it adds a BENCHMARK_UNREACHABLE macro to assist
in documenting/catching unreachable code paths.

* Rename ValueUnion accessors.

Define BENCHMARK_OS_NETBSD for NetBSD.

Add detection of cpuinfo_cycles_per_second and cpuinfo_num_cpus.
This code shared detection of these properties with FreeBSD.

Fixes #479