[vm/ubsan] Fix NO_SANITIZE_UNDEFINED definition.

This is a follow-up to 61c3fbc220 to make it accomodate android builds.

Fixes https://ci.chromium.org/ui/p/dart/builders/ci.sandbox/vm-ffi-android-product-arm64c/10387 breakage.
TEST=ci

Change-Id: I0d18446014516b7de94ca1ed7336c0b98d699ee6
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/471324
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>

runtime/platform/undefined_behavior_sanitizer.h

@@ -5,6 +5,10 @@
 #ifndef RUNTIME_PLATFORM_UNDEFINED_BEHAVIOR_SANITIZER_H_
 #define RUNTIME_PLATFORM_UNDEFINED_BEHAVIOR_SANITIZER_H_
 
+#ifdef __clang__
+#define NO_SANITIZE_UNDEFINED(check) [[clang::no_sanitize(check)]]
+#else
 #define NO_SANITIZE_UNDEFINED(check) [[gnu::no_sanitize(check)]]
+#endif
 
 #endif  // RUNTIME_PLATFORM_UNDEFINED_BEHAVIOR_SANITIZER_H_