Removes unused function for non-MS compilers.

Summary:
When building without Microsoft Visual C++, `do_nothing` is not used
at all, potentially triggering unused function warnings, which makes it useless
to compile with strict flags such as `-Wall -Werror`.

Reviewed By: yfeldblum, aary

Differential Revision: D14843227

fbshipit-source-id: 28f0041ccae8bf07dc1f3e41e1cf67291c3d8447

folly/synchronization/SanitizeThread.cpp

@@ -42,12 +42,8 @@ extern "C" FOLLY_ATTR_WEAK void AnnotateBenignRaceSized(
     long size,
     const char* desc);
 
-namespace {
-void do_nothing(...) {}
-} // namespace
-
 #if _MSC_VER
-#define FOLLY_SANITIZE_THREAD_CALL_HOOK(name, ...) do_nothing(__VA_ARGS__)
+#define FOLLY_SANITIZE_THREAD_CALL_HOOK(name, ...) [](...) {}(__VA_ARGS__)
 #else
 #define FOLLY_SANITIZE_THREAD_CALL_HOOK(name, ...) name(__VA_ARGS__)
 #endif