Driver: do not strip file extensions when printing diagnostics.

Before: clang-3: error: no input files
After:  clang-3.3: error: no input files

This means that we'll also print clang.exe on windows, but I don't see a problem
with that.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@176788 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/tools/driver/driver.cpp b/tools/driver/driver.cpp
index de627fb..c879017 100644
--- a/tools/driver/driver.cpp
+++ b/tools/driver/driver.cpp
@@ -417,7 +417,7 @@
   // DiagnosticOptions instance.
   TextDiagnosticPrinter *DiagClient
     = new TextDiagnosticPrinter(llvm::errs(), &*DiagOpts);
-  DiagClient->setPrefix(llvm::sys::path::stem(Path.str()));
+  DiagClient->setPrefix(llvm::sys::path::filename(Path.str()));
   IntrusiveRefCntPtr<DiagnosticIDs> DiagID(new DiagnosticIDs());
 
   DiagnosticsEngine Diags(DiagID, &*DiagOpts, DiagClient);