* timestamp: use rfc3339-formatted timestamps in output

Replace localized timestamps with machine-readable IETF RFC 3339 format
timestamps. This is an attempt to make the output timestamps easily
machine-readable. ISO8601 specifies standards for time interchange
formats. IETF RFC 3339: https://tools.ietf.org/html/rfc3339 defines a
subset of these for use in the internet. The general form for these
timestamps is:

YYYY-MM-DDTHH:mm:SS[+-]hhmm

This replaces the localized time formats that are currently being used
in the benchmark output to prioritize interchangeability and
machine-readability.

This might break existing programs that rely on the particular date-time
format. This might also may make times less human readable. RFC3339 was
intended to balance human readability and simplicity for machine
readability, but it is primarily intended as an internal representation.

* timers: remove utc string formatting

We only ever need local time printing. Remove the UTC printing
and cosnolidate the logic slightly.

* timers: manually create rfc3339 string

The C++ standard library does not output the time offset in RFC3339
format, it is missing the : between hours and minutes. VS does not
appear to support timezone information by default. To avoid adding too
much complexity to benchmark around timezone handling e.g. a full
date library like https://github.com/HowardHinnant/date, we fall back
to outputting GMT time with a -00:00 offset for those cases.

* timers: use reentrant form for localtime_r & tmtime_r

For non-windows, use the reentrant form for the time conversion
functions.

* timers: cleanup

Use strtol instead of brittle moving characters around.

* timers: only call strftime twice.

Also size buffers to known maximum necessary size and name constants
more appropriately.

* timers: fix unused variable warning

* Use ==/!= to compare constant literals (str, bytes, int, float, tuple)

Avoid Syntax Warning on Python 3.8: `3 is 3`  # —> Syntax Warning

* Delete mingw.py

* Add Python bindings.

* Add license headers.

* Change example to a test.

* Add example usage to module docstring.

* Add missing <cerrno> header

This commit fixes a current build error on Android where 'errno' is an unidentified
symbol due to a missing header

* Update string_util.cc

Conditionally adds <cerrno> if BENCHMARK_STL_ANDROID_GNUSTL is defined

In a previous commit[1], diagnostic pragmas were used to avoid this
warning. However, the incorrect warning flag was indicated, leaving the
warning in place. -Wdeprecated is for deprecated features while
-Wdeprecated-declarations for deprecated functions, variables, and
types[2].

[1] c4084619
[2] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Fixes the following issues with the implementation of `cycleclock::Now`:

- The RISC-V implementation wouldn't compile due to a typo;

- Both the PPC and RISC-V implementation's asm statements lacked the
  volatile keyword. This resulted in the repeated read of the counter's
  high part being optimized away, so overflow wasn't handled at all.
  Multiple counter reads could also be misoptimized, especially in LTO
  scenarios.

- Relied on the zero/sign-extension of inline asm operands, which isn't
  guaranteed to occur and differs between compilers, namely GCC and Clang.

The PowerPC64 implementation was improved to do a single 64-bit read of
the time-base counter.

The RISC-V implementation was improved to do the overflow handing in
assembly, since Clang would generate a branch, defeating the purpose
of the non-branching counter reading approach.

* Fix type conversion warnings.

Fixes #949

Tested locally (Linux/clang), but warnings are on MSVC so may differ.

* Drop the ULP so the double test passes

Line "- /usr/local/bin:$PATH" is misformatted.
It must be something like "- PATH=/usr/local/bin:$PATH".

It seems something changed in tarvis-ci month ago and now this leads to:

Setting environment variables from .travis.yml
$ export PATH=

Defailt PATH is /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin
so already containts /usr/local/bin.


Image "xcode8.3" contains macOS 10.12 (sierra) which has no bottles
with precompiled gcc-7 in homebrew storage.

Image "xcode9.4" is a current default with macOS 10.13 (high_sierra).

Link: https://docs.travis-ci.com/user/reference/osx/
Link: https://formulae.brew.sh/formula/gcc@7Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

This reverts commit 5ce2429a.

Reverts https://github.com/google/benchmark/pull/923
Reopens https://github.com/google/benchmark/issues/922
Fixes https://github.com/google/benchmark/issues/928
Closes https://github.com/google/benchmark/pull/930

See discussion in https://github.com/google/benchmark/issues/928
this broke pkg-config support, since there we don't account
for the suffix, nor is it trivial to do so.

This reverts commit 5ce2429a.

Reverts https://github.com/google/benchmark/pull/923
Reopens https://github.com/google/benchmark/issues/922
Fixes https://github.com/google/benchmark/issues/928
Closes https://github.com/google/benchmark/pull/930

See discussion in https://github.com/google/benchmark/issues/928
this broke pkg-config support, since there we don't account
for the suffix, nor is it trivial to do so.

* Add State::error_occurred()

* Relax CHECK condition in benchmark_runner.cc

If the benchmark state contains an error, do not expect any iterations has been run.
This allows using SkipWithError() and return early from the benchmark function.

* README.md: document new possible usage of SkipWithError()

This fixes the Visual Studio 2019 warning:

`C4244: '=': conversion from 'int' to 'char', possible loss of data`

When implicitly casting the return value of tolower() (int) to char.

Fixes: #932

* add Jordan Williams to both CONTRIBUTORS and AUTHORS

* alias benchmark libraries

Provide aliased CMake targets for the benchmark and benchmark_main targets.
The alias targets are namespaced under benchmark::, which is the namespace when they are exported.
I chose not to use either the PROJECT_NAME or the namespace variable but to hard-code the namespace.
This is because the benchmark and benchmark_main targets are hard-coded by name themselves.
Hard-coding the namespace is also much cleaner and easier to read.

* link to aliased benchmark targets

It is safer to link against namespaced targets because of how CMake interprets the double colon.
Typo's will be caught by CMake at configuration-time instead of during compile / link time.

* document the provided alias targets

* add "Usage with CMake" section in documentation

This section covers linking against the alias/import CMake targets and including them using either find_package or add_subdirectory.

* format the "Usage with CMake" README section

Added a newline after the "Usage with CMake" section header.
Dropped the header level of the section by one to make it a direct subsection of the "Usage" section.
Wrapped lines to be no longer than 80 characters in length.

* Add DEBUG_POSTFIX to libraries.

Makes it possible to install Debug and Release versions on the
same system. Without this, there were only linker errors when using
the wrong configuration.

* Update CONTRIBUTORS and AUTHORS according to guide

As disscussed in https://github.com/google/benchmark/issues/899,
it is all but certain that the multiplier should be 1024, not 1000.

Fixes https://github.com/google/benchmark/issues/899

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

Fix some issues seen in some static analysis reports

Higher up we dereference argc only if it is not null.
But here we do no such check.

From clang-tidy bugprone-incorrect-roundings check:
> casting (double + 0.5) to integer leads to incorrect rounding; consider using lround (#include <cmath>) instead

From clang-tidy bugprone-incorrect-roundings check:
> casting (double + 0.5) to integer leads to incorrect rounding; consider using lround (#include <cmath>) instead

* CTest must use proper paths to executables

With the following syntax:

```
  add_test(NAME <name> COMMAND <command> [<arg>...])
```

if `<command>` specifies an executable target it will automatically
be replaced by the location of the executable created at build time.

This is important if a `<Configuration>_POSTFIX` like `_d` is used.

* Fix typo in ctest invocation

Instead of `-c` the uppercase `-C` must be used to select a config.
But better use the longopt.