Refactor builtin available to macro

Author: cjappl

compiler-rt/lib/rtsan/tests/rtsan_test_interceptors_posix.cpp

@@ -120,16 +120,19 @@ TEST(TestRtsanInterceptors, VallocDiesWhenRealtime) {
   ExpectNonRealtimeSurvival(Func);
 }
 
+#if __has_builtin(__builtin_available) && SANITIZER_APPLE
+#define ALIGNED_ALLOC_AVAILABLE() __builtin_available(macOS 10.15, *)
+#else
+// We are going to assume this is true until we hit systems where it isn't
+#define ALIGNED_ALLOC_AVAILABLE() true
+#endif
+
 TEST(TestRtsanInterceptors, AlignedAllocDiesWhenRealtime) {
-#if SANITIZER_APPLE
-  if (__builtin_available(macOS 10.15, *)) {
-#endif // SANITIZER_APPLE
+  if (ALIGNED_ALLOC_AVAILABLE()) {
     auto Func = []() { EXPECT_NE(nullptr, aligned_alloc(16, 32)); };
     ExpectRealtimeDeath(Func, "aligned_alloc");
     ExpectNonRealtimeSurvival(Func);
-#if SANITIZER_APPLE
   }
-#endif
 }
 
 // free_sized and free_aligned_sized (both C23) are not yet supported