CXXFLAGS
--------

Default compilation flags to be used when compiling ``CXX`` (C++) files. Will
only be used by CMake on the first configuration to determine ``CXX`` default
compilation flags, after which the value for ``CXXFLAGS`` is stored in the cache
as :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>`. For any configuration run (
including the first), the environment variable will be ignored if
the :variable:`CMAKE_CXX_FLAGS <CMAKE_<LANG>_FLAGS>` variable is defined.