Make -save-temps=obj play better with -o.

Use only the *dirname* of the pathname given to -o, so that -o can still be used
to name the output executable. This is more like what GCC 4.5 does.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74790 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CompilerDriver/Main.cpp

@@ -37,6 +37,7 @@ namespace {
     }
     else if (SaveTemps == SaveTempsEnum::Obj && !OutputFilename.empty()) {
       tempDir = OutputFilename;
+      tempDir = tempDir.getDirname();
 
       if (!tempDir.exists()) {
         std::string ErrMsg;