Both GFLAGS_NAMESPACE and GFLAGS_INCLUDE_DIR can be used to customize the installation of the gflags library. One specifies the C++ namespace name of the gflags symbols, the other the include subdirectory path of the public header files. By default, both are set to "gflags", but other Google libraries still expect "google" as C++ namespace name, but not necessarily also include path.

Both GFLAGS_NAMESPACE and GFLAGS_INCLUDE_DIR can be used to customize the installation of the gflags library. One specifies the C++ namespace name of the gflags symbols, the other the include subdirectory path of the public header files. By default, both are set to "gflags", but other Google libraries still expect "google" as C++ namespace name, but not necessarily also include path.

Change version to 2.1.0, i.e., use common semantic versioning system including patch number for bug fix releases.

Add link dependency on shlwapi.lib during build configuration instead of #pragma comment statement. Use this library also on MinGW.

The OS_WINDOWS #define has previously been used in gflags.cc before the CMake migration.

Expose as few system variables as possible through public interface.
Perform STRIP_FLAGS_HELP test using CMake instead of Bash.
Change file path separator used by gflags_reporting.cc to backslash on Windwos.

* C language definition is needed for CheckForPthreads.c

This eases integration with other applications making use
of gflags without needing to install it in the system.
find_package looks in the registry for existing software.