When building on Windows with `BUILD_SHARED_LIBS=ON`, the symbols were
not being properly exported in the DLL. Fix this by setting
`CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS`.

Fixes #888 

Initialize option flags from environment variables values if they are defined, eg. `BENCHMARK_OUT=<filename>` for `--benchmark_out=<filename>`. Command line flag value always prevails.

Fixes https://github.com/google/benchmark/issues/881.

While I'm here, format all of the files that I touched.

When cross-compiling, this variable was not set on the second run
of CMake, resulting in the next check failing even though it shouldn't
be run in the first place. Fix this by caching the variable.

* fixed the param order in g++ command and fixed the path for -L

* reorder the parameters for g++ command

This macro is sometimes already defined and redefining it results
in build errors.

These OS's don't always have HOST_NAME_MAX defined, resulting in
build errors.

A few related changes as well:
* Only define HOST_NAME_MAX if it's not already defined. There are
  some cases where this is already defined, e.g. with NaCl if
  __USE_POSIX is set. To avoid all of these, only define it if it's
  not already defined.
* Default HOST_NAME_MAX to 64 and issue a #warning. Having the wrong
  max length is pretty harmless. The name just ends up getting
  truncated and this is only for printing debug info. Because we're
  constructing a std::string from a char[] (so defined length), we
  don't need to worry about gethostname's undefined behavior for
  whether the truncation is null-terminated when the hostname
  doesn't fit in HOST_NAME_MAX. Of course, this doesn't help people
  who have -Werror set, since they'll still get a warning.

* Fix missing paren in README code sample, and fix code spacing.

* Add Colin Braley to AUTHORS and CONTRIBUTORS.

* Guard ASSERT_THROWS checks with BENCHMARK_HAS_NO_EXCEPTIONS

This allows the test be run with exceptions turned off

* Add myself to CONTRIBUTORS

I don't need to be added to AUTHORS, as I am a Google employee

* Update with instructions to build under Visual Studio

Fixes Issue #634.

I spent 3 days trying to build this library under Visual Studio 2017, only to discover on has to link to `Shlwapi.lib`.

Became so frustrated with the docs that I added full build instructions for Visual Studio 2015, 2017 and Intel Comiler 2015 and 2019.

* Update headings

In `cmake/GoogleTest.cmake`, GOOGLETEST_PATH is default-initialized, but that init forgot to
account for the fact that the patch is explicitly supposed to be user-configurable.
By passing `CACHE` to `set()` we avoid that error.

- Adresses : #856

  - The unused `doc` argument was removed from the `DEFINE_` macros in
    `commandlineflags.h`

  - Converted all the previous `doc` strings passed to the `DEFINE_`
    macros to multiline comments.

- Addresses : #858

  - Rule `*.swp` is added to `.gitignore` to ensure that the vim temporary
    `.swp` backup files are ignored and they don't pollute the results of
    `git status -u`.

Documentation of basic use of `DenseRange` was added to README.md.

VS2013 is unsupported since https://github.com/google/benchmark/pull/691 / https://github.com/google/benchmark/commit/eb8cbec0776455463274ea9947ab0ecfe0f768fe
but i forgot to update docs.
References:
* https://github.com/google/benchmark/issues/689
* https://github.com/google/benchmark/pull/691
* https://github.com/google/googletest/pull/1815
* https://github.com/google/benchmark/issues/853
* https://github.com/google/benchmark/pull/854

While current counters can e.g. answer the question
"how many items is processed per second", it is impossible to get
it to tell "how many seconds it takes to process a single item".

The solution is to add a yet another modifier `kInvert`,
that is *always* considered last, which simply inverts the answer.

Fixes #781, #830, #848.

The CSVReporter is deprecated, but we still need to reference it in
a few places. To avoid breaking the build when warnings are errors,
we need to disable the warning when we do so.

* Corrected the installation procedure

Now it can be put into a script.

* Updated the file tree

Necessary after installation instruction change

* corrected cmake commands

* Update README.md

* Update AUTHORS and CONTRIBUTORS

* Fix WSL self-test failures

Some of the benchmark self-tests expect and check for a particular
output format from the benchmark library. The numerical values must
not be infinity or not-a-number, or the test will report an error.
Some of the values are computed bytes-per-second or items-per-second
values, so these require that the measured CPU time for the test to be
non-zero. But the loop that is being measured was empty, so the
measured CPU time for the loop was extremely small. On systems like
Windows Subsystem for Linux (WSL) the timer doesn't have enough
resolution to measure this, so the measured CPU time was zero.

This fix just makes sure that these tests have something within the
timing loop, so that the benchmark library will not decide that the
loop takes zero CPU time. This makes these tests more robust, and in
particular makes them pass on WSL.

The filenames are consistently inconsistent in windows world, might
have something to do with default file system being case-insensitive.
While the native MinGW buils were fixed in 52613079
that only addressed the headers, but not libraries.
The problem remains when one tries to do a MinGW cross-build from
case-sensitive filesystem.

The RISC-V implementation of `cycleclock::Now` uses the user-space
`rdcycle` instruction to query how many cycles have happened since the
core started.

The only complexity here is on 32-bit RISC-V, where `rdcycle` can only
read the lower 32 bits of the 64-bit hardware counter. In this case,
`rdcycleh` reads the higher 32 bits of the counter. We match the powerpc
implementation to detect and correct for overflow in the high bits.

and ThreadManager ctor explicit.

Reported by CppCheck.

Found in -UNDEBUG build

This is a shameless rip-off of https://github.com/google/benchmark/pull/646
I did promise to look into why that proposed PR was producing
so much worse assembly, and so i finally did.

The reason is - that diff changes `size_t` (unsigned) to `int64_t` (signed).

There is this nice little `assert`:
https://github.com/google/benchmark/blob/7a1c37028359ca9d386d719a6ad527743cf1b753/include/benchmark/benchmark.h#L744
It ensures that we didn't magically decide to advance our iterator
when we should have finished benchmarking.

When `cached_` was unsigned, the `assert` was `cached_ UGT 0`.
But we only ever get to that `assert` if `cached_ NE 0`,
and naturally if `cached_` is not `0`, then it is bigger than `0`,
so the `assert` is tautological, and gets folded away.

But now that `cached_` became signed, the assert became `cached_ SGT 0`.
And we still only know that `cached_ NE 0`, so the assert can't be
optimized out, or at least it doesn't currently.

Regardless of whether or not that is a bug in itself,
that particular diff would have regressed the normal 64-bit systems,
by halving the maximal iteration space (since we go from unsigned counter
to signed one, of the same bit-width), which seems like a bug.
And just so it happens, fixing *this* bug, fixes the other bug.

This produces fully (bit-by-bit) identical state_assembly_test.s
The filecheck change is actually needed regardless of this patch,
else this test does not pass for me even without this diff.

This may or may not have gotten broken now that benchmark was marked as CXX-only.

This will make CMake skip all the checks for C compiler.

Android doesn't support `getloadavg`

Weird, but seems consistent with the rest of cmake here.

This allows a project to include both googletest and benchmark as top-level git submodule.

This allows incorporating Benchmark to an existing CMake project that already incorporates googletest.
https://github.com/google/googletest/blob/master/googletest/README.md#incorporating-into-an-existing-cmake-project
https://github.com/abseil/abseil-cpp/tree/master/CMake#incorporating-abseil-into-a-cmake-project

* Add support for GNU Install Dirs from GNU Coding Standards

* src/CMakeLists.txt: Added support for setting the standard variables,
                      such as CMAKE_INSTALL_BINDIR.

* Replace install destinations by the ones from GNU Coding Standards.

* Set the default .cmake and .pc default path.

Very interesting, i was completely not expecting to see that cmake
failure from https://github.com/google/benchmark/pull/801 *here*.

This reverts commit 7da47d03.

Generally we can't just add -m32 in the middle of the build.
It currently just happens to work, but that is not guaranteed.

It was looking in `"<...>/googlebenchmark/build/third_party/googletest"`,
with these extra `"` quotes, and wasn't finding anything..

https://github.com/google/benchmark/pull/801 is stuck with some cryptic cmake failure due to
some linking issue between googletest and threading libraries.

I suspect that is mostly happening because of the, uhm,
intentionally extremely twisted-in-the-brains approach that is being used to
actually build the library as part of the buiild,
except without actually building it as part of the build.

If we do actually build it as part of the build,
then all the transitive dependencies should magically be in order,
and maybe everything will just work.

This new version of cmake magic was written by me in
https://github.com/darktable-org/rawspeed/blob/0e22f085c57cd629983c7351c598abd744b421b5/cmake/Modules/GoogleTest.cmake.in
https://github.com/darktable-org/rawspeed/blob/0e22f085c57cd629983c7351c598abd744b421b5/cmake/Modules/GoogleTest.cmake, based on the official googletest docs and LOTS of experimentation.

* Update and organize README

* Update AUTHORS and CONTRIBUTORS

Fixes #803.