enable FOLLY_DISABLE_UNDEFINED_BEHAVIOR_SANITIZER macro in ASAN

Summary:
It's common to use UBSAN with ASAN at the same time, and we'll merge them eventually too. As a result we can check for ASAN defined macros to conditionally compile code for UBSAN.

We still have a few build modes that use standalone UBSAN, and unlike other sanitizers, UBSAN doesn't define a magic macro that we could use. In the past we added UNDEFINED_SANITIZER to our compiler flags, but I'd like to go away from it towards a more standard solution (eg check for ASAN).

Reviewed By: yfeldblum, luciang

Differential Revision: D6931054

fbshipit-source-id: 4b298d1cd72cecd693bf99eda309568ef019c544

folly/CPortability.h

@@ -108,22 +108,12 @@
 #define FOLLY_SANITIZE 1
 #endif
 
-/**
- * ASAN/MSAN/TSAN define pre-processor symbols:
- * ADDRESS_SANITIZER/MEMORY_SANITIZER/THREAD_SANITIZER.
- *
- * UBSAN doesn't define anything and makes it hard to
- * conditionally compile.
- *
- * The build system should define UNDEFINED_SANITIZER=1 when UBSAN is
- * used as folly whitelists some functions.
- */
-#if UNDEFINED_SANITIZER
+#if FOLLY_SANITIZE
 #define FOLLY_DISABLE_UNDEFINED_BEHAVIOR_SANITIZER(...) \
   __attribute__((no_sanitize(__VA_ARGS__)))
 #else
 #define FOLLY_DISABLE_UNDEFINED_BEHAVIOR_SANITIZER(...)
-#endif // UNDEFINED_SANITIZER
+#endif // FOLLY_SANITIZE
 
 /**
  * Macro for marking functions as having public visibility.