cmake _MK_HAVE_STDLIB_H examples

JulNadeauCA/libagar CMakeChecks.cmake :3111

check_c_source_compiles("
#include <stdlib.h>
int main(int argc, char *argv[]) {
	void *foo = malloc(1);
	free(foo);
	return (0);
}
" _MK_HAVE_STDLIB_H)