check_c_source_compiles("
volatile int glo = 1234;
int foo(int) __attribute__ ((pure));
int foo(int x) { return (x*x + glo); }
int main(int argc, char *argv[])
{
	int x = foo(1);
	glo = 2345;
	x = foo(2);
	return (x);
}
" HAVE_PURE_ATTRIBUTE)