CMake/Modules/Compiler/GNU-C-FeatureTests.cmake

set(_cmake_oldestSupported "(__GNUC__ * 100 + __GNUC_MINOR__) >= 407")

set(GNU46_C11 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L")
set(_cmake_feature_test_c_static_assert "${GNU46_C11}")
# Since 4.4 at least:
set(GNU44_C99 "${_cmake_oldestSupported} && defined(__STDC_VERSION__) && __STDC_VERSION__ >= 199901L")
set(_cmake_feature_test_c_restrict "${GNU44_C99}")
set(_cmake_feature_test_c_variadic_macros "${GNU44_C99}")

set(GNU_C90 "${_cmake_oldestSupported} && !defined(__STDC_VERSION__)")
set(_cmake_feature_test_c_function_prototypes "${GNU_C90}")