Ubuntu 16.04 is end-of-life, we're going to remove it from Bazel CI.

If you like you can add testing on `ubuntu2004` platform which we also support.

cmake: export `<atomic>` availability (fixes #667)

cmake: allow to override `-fPIC`

cmake: fixed msvc snprintf detection (fixes #668)

By exporting `COPYING`, Bazel projects depending on glog can easily access its license.

Allow updating vmodule levels after vmodule level has been cached

vmodule flag is relevant for GNUC environments only.

Fix cmake configuration for cygwin environment

1. Use CYGWIN variable to test for WIN32 because WIN32 var has been deprecated in later versions of cmake.
2. Translate TEST_SRC_DIR to windows paths because posix open calls can not handle unix-like paths in cygwin environment.

Expose `IsGoogleLoggingInitialized()` in public API.

Usually library does not have control of the process lifespan.
Without this function, it is impossible to init/shutdown reliably.
It has been one of the major pain points for years when using glog in libraries.

AFAIK 3 workarounds have been used previously:
1. Init without checking. This causes compatiblity issues with other libs using glog.
2. Also provide a init function in library's API. This makes API complicated and stateful, especially for libs that does not mean to stay for the entire life of process.
3. Steal the utility function in internal namespace. Does not work with msvc (due to missing dllexport) or `gcc -fvisibility=hidden`.

None of them are perfect, except for the last hack that usually works well on Linux.
0.5.0 changes default visibility to hidden and it does not work anymore.

Resolve https://github.com/google/glog/issues/125

Also, add a sha256 for gflags to avoid a build warning.

release 0.5

readme: update CMake source directory option

The `-H` command-line option has been replaced in 3.13 by `-S`.

CHECK support for nullptr (fixes #341)

fix LogCleaner::IsLogFromCurrentProject for filename_extension

fix gflags windows linker warnings

Add support for customizing the prefix format

This allows CHECK_NE(foo, nullptr) to compile and produces "nullptr" for the
string representation of nullptr.

cmake: allow to disable symbolize

fixed windows builds

Add Windows builds using GitHub Actions

Add VS 2017, VS 2019 and MinGW-w64 builds running the test cases. All
compiler have build jobs for C++11 and C++17.

Currently only the build-type 'Debug' is used, but can easily be
extended to build both 'Debug' and 'Release'.

removed windows-specific headers

Use generated config.h for Windows.

This unblocks a simplification of the Windows CMake build.

fixed file extension

cmake: build shared libs by default