Add MSVC macro

Co-authored-by: Alex Reinking <[email protected]>

test/correctness/saturating_casts.cpp

@@ -291,7 +291,7 @@ void test_one_source() {
 
 int main(int argc, char **argv) {
 
-#ifdef __i386__
+#if defined(__i386__) || defined(_M_IX86)
     printf("[SKIP] Skipping test because it requires bit-exact int to float casts,\n"
            "and on i386 without SSE it is hard to guarantee that the test binary won't use x87 instructions.\n");
     return 0;