try un-teaching TSAN about Mac semaphores

Now using dispatch_semaphore_t, maybe it already knows?

Change-Id: I65499ceaee195293541a37704ae424bbee7c8740
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248456
Auto-Submit: Mike Klein <mtklein@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>

Author: Mike Klein

src/core/SkSemaphore.cpp

@@ -11,34 +11,14 @@
 #if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
     #include <dispatch/dispatch.h>
 
-    // We've got to teach TSAN that there is a happens-before edge between
-    // dispatch_semaphore_signal() and dispatch_semaphore_wait().
-    #if __has_feature(thread_sanitizer)
-        extern "C" void AnnotateHappensBefore(const char*, int, void*);
-        extern "C" void AnnotateHappensAfter (const char*, int, void*);
-    #else
-        static void AnnotateHappensBefore(const char*, int, void*) {}
-        static void AnnotateHappensAfter (const char*, int, void*) {}
-    #endif
-
     struct SkSemaphore::OSSemaphore {
         dispatch_semaphore_t fSemaphore;
 
-        OSSemaphore()  {
-            fSemaphore = dispatch_semaphore_create(0/*initial count*/);
-        }
+        OSSemaphore()  { fSemaphore = dispatch_semaphore_create(0/*initial count*/); }
         ~OSSemaphore() { dispatch_release(fSemaphore); }
 
-        void signal(int n) {
-            while (n-- > 0) {
-                AnnotateHappensBefore(__FILE__, __LINE__, &fSemaphore);
-                dispatch_semaphore_signal(fSemaphore);
-            }
-        }
-        void wait() {
-            dispatch_semaphore_wait(fSemaphore, DISPATCH_TIME_FOREVER);
-            AnnotateHappensAfter(__FILE__, __LINE__, &fSemaphore);
-        }
+        void signal(int n) { while (n --> 0) { dispatch_semaphore_signal(fSemaphore); } }
+        void wait() { dispatch_semaphore_wait(fSemaphore, DISPATCH_TIME_FOREVER); }
     };
 #elif defined(SK_BUILD_FOR_WIN)
     struct SkSemaphore::OSSemaphore {