[Support] Add TimeTraceScope constructor without detail arg

This simplifies code where no extra details are required
Also don't write out detail when it is empty.

Differential Revision: https://reviews.llvm.org/D71347
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 8d59729..c5bf6fe 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -924,8 +924,7 @@
   }
 
   {
-    llvm::TimeTraceScope TimeScope("PerformPendingInstantiations",
-                                   StringRef(""));
+    llvm::TimeTraceScope TimeScope("PerformPendingInstantiations");
     PerformPendingInstantiations();
   }