This is a CMake Environment Variable. Its initial value is taken from the calling process environment.
Add default compilation flags to be used when compiling
CMake uses this environment variable value, in combination with its own
builtin default flags for the toolchain, to initialize and store the
CMAKE_C_FLAGS cache entry.
This occurs the first time a build tree is configured for language
For any configuration run (including the first), the environment variable
will be ignored if the
CMAKE_C_FLAGS variable is already defined.