cmake: Respect CMAKE_REQUIRED_* variables in CHECK_C_COMPILER_FLAG_SSP

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

cmake/Modules/CheckCCompilerFlagSSP.cmake

@@ -16,11 +16,14 @@
 # For details see the accompanying COPYING-CMAKE-SCRIPTS file.
 
 
+include_guard(GLOBAL)
 include(CheckCSourceCompiles)
 
-function(CHECK_C_COMPILER_FLAG_SSP _FLAG _RESULT)
+macro(CHECK_C_COMPILER_FLAG_SSP _FLAG _RESULT)
    set(SAFE_CMAKE_REQUIRED_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}")
    set(CMAKE_REQUIRED_DEFINITIONS "${_FLAG}")
+
    check_c_source_compiles("int main(int argc, char **argv) { char buffer[256]; return buffer[argc]=0;}" ${_RESULT})
+
    set(CMAKE_REQUIRED_DEFINITIONS "${SAFE_CMAKE_REQUIRED_DEFINITIONS}")
-endfunction(CHECK_C_COMPILER_FLAG_SSP)
+endmacro(CHECK_C_COMPILER_FLAG_SSP)