Bug 1307590 - Check that clang supports the no_sanitize attribute r=mt

https://nss-dev.phacility.com/D70

lib/freebl/blapii.h

@@ -44,10 +44,18 @@ SEC_END_PROTOS
 #define HAVE_UNALIGNED_ACCESS 1
 #endif
 
-#if defined(__clang__) && defined(HAVE_UNALIGNED_ACCESS)
+#if defined(__clang__)
+#define HAVE_NO_SANITIZE_ATTR __has_attribute(no_sanitize)
+#else
+#define HAVE_NO_SANITIZE_ATTR 0
+#endif
+
+#if defined(HAVE_UNALIGNED_ACCESS) && HAVE_NO_SANITIZE_ATTR
 #define NO_SANITIZE_ALIGNMENT __attribute__((no_sanitize("alignment")))
 #else
 #define NO_SANITIZE_ALIGNMENT
 #endif
 
+#undef HAVE_NO_SANITIZE_ATTR
+
 #endif /* _BLAPII_H_ */