tweak FOLLY_LIKELY to accept complex expressions

Summary: Complex expressions involving certain tokens parse at preprocessor time as multiple preprocessor arguments. Quite awkward. The trick is to change the preprocessor macro to deal in variadic arguments.

Reviewed By: ot, Orvid, luciang

Differential Revision: D27986071

fbshipit-source-id: a126fca260396418b14b7367e3e41ddeea78b7af

folly/Likely.h

@@ -38,8 +38,8 @@
 //    blocks which unconditionally call [[noreturn]]-annotated functions. Such
 //    cases do not require likeliness annotations.
 
-#define FOLLY_LIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 1)
-#define FOLLY_UNLIKELY(x) FOLLY_DETAIL_BUILTIN_EXPECT((x), 0)
+#define FOLLY_LIKELY(...) FOLLY_DETAIL_BUILTIN_EXPECT((__VA_ARGS__), 1)
+#define FOLLY_UNLIKELY(...) FOLLY_DETAIL_BUILTIN_EXPECT((__VA_ARGS__), 0)
 
 //  Un-namespaced annotations