Add Diagnostic::Report method for reporting diagnostics without a location.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@86760 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/Warnings.cpp b/lib/Frontend/Warnings.cpp
index 7b01b0f..3f442c8 100644
--- a/lib/Frontend/Warnings.cpp
+++ b/lib/Frontend/Warnings.cpp
@@ -100,8 +100,7 @@
     }
 
     if (Diags.setDiagnosticGroupMapping(OptStart, Mapping))
-      Diags.Report(FullSourceLoc(), diag::warn_unknown_warning_option)
-        << ("-W" + Opt);
+      Diags.Report(diag::warn_unknown_warning_option) << ("-W" + Opt);
   }
 
   return false;