clang-cl: print diagnostics as "error(clang): foo" in /fallback mode

This solves two problems:

1) MSBuild will not flag the build as unsuccessful just because we print
   an error in the output, since "error(clang):" doesn't seem to match
   the regex it's using.

2) It becomes more clear that the diagnostic is coming from clang as
   supposed to cl.exe.

Differential Revision: http://llvm-reviews.chandlerc.com/D1735

llvm-svn: 191250
diff --git a/clang/lib/Frontend/TextDiagnosticPrinter.cpp b/clang/lib/Frontend/TextDiagnosticPrinter.cpp
index c22798a..994a8f7 100644
--- a/clang/lib/Frontend/TextDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/TextDiagnosticPrinter.cpp
@@ -132,7 +132,8 @@
   // diagnostics in a context that lacks language options, a source manager, or
   // other infrastructure necessary when emitting more rich diagnostics.
   if (!Info.getLocation().isValid()) {
-    TextDiagnostic::printDiagnosticLevel(OS, Level, DiagOpts->ShowColors);
+    TextDiagnostic::printDiagnosticLevel(OS, Level, DiagOpts->ShowColors,
+                                         DiagOpts->CLFallbackMode);
     TextDiagnostic::printDiagnosticMessage(OS, Level, DiagMessageStream.str(),
                                            OS.tell() - StartOfLocationInfo,
                                            DiagOpts->MessageLength,