[gn build] hook up tsan on macOS too

Mostly just works already.

llvm/utils/gn/secondary/compiler-rt/lib/BUILD.gn

@@ -3,9 +3,6 @@ group("lib") {
     "//compiler-rt/lib/asan",
     "//compiler-rt/lib/builtins",
     "//compiler-rt/lib/profile",
+    "//compiler-rt/lib/tsan" ,
   ]
-  if (target_os == "linux") {
-    # FIXME: Make work on macOS.
-    deps += [ "//compiler-rt/lib/tsan" ]
-  }
 }

llvm/utils/gn/secondary/compiler-rt/lib/tsan/BUILD.gn

@@ -145,12 +145,7 @@ target(tsan_target_type, "tsan") {
     ldflags = [
       "-lc++",
       "-lc++abi",
-
-      # tsan
-      # FIXME
-
-      # ubsan
-      "-Wl,-U,___ubsan_default_options",
+      "-lobjc",
 
       # sanitizer_common
       "-Wl,-U,___sanitizer_free_hook",