win: Omit ".exe" from clang and clang-cl driver-level diagnostics.

Like https://reviews.llvm.org/D51133 but for clang.
https://reviews.llvm.org/D51134


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@340498 91177308-0d34-0410-b5e6-96231b3b80d8

tools/driver/driver.cpp

@@ -260,9 +260,9 @@ static void FixupDiagPrefixExeName(TextDiagnosticPrinter *DiagClient,
                                    const std::string &Path) {
   // If the clang binary happens to be named cl.exe for compatibility reasons,
   // use clang-cl.exe as the prefix to avoid confusion between clang and MSVC.
-  StringRef ExeBasename(llvm::sys::path::filename(Path));
-  if (ExeBasename.equals_lower("cl.exe"))
-    ExeBasename = "clang-cl.exe";
+  StringRef ExeBasename(llvm::sys::path::stem(Path));
+  if (ExeBasename.equals_lower("cl"))
+    ExeBasename = "clang-cl";
   DiagClient->setPrefix(ExeBasename);
 }