The CHECK_C_COMPILER_FLAG() and CHECK_CXX_COMPILER_FLAG() functions
from CMake return the result of the test in a variable passed as an
This variable is cached internally, so that subsequent calls of the
function with the same variable return the result without performing the
The add_c_compiler_flag() and add_cxx_compiler_flag() functions are
calling CHECK_C_COMPILER_FLAG() and CHECK_CXX_COMPILER_FLAG() with
the same variable FLAG_IS_SUPPORTED, making the test ineffective.
This diffs fixes the issue by generating a new variable name based on
the flag name. This allow for keeping advantage of the caching
mechanisme while having a different variable for each flag, making the
test working as expected.