CFLAGS
------

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