Accept -x objc++-cpp-output as an alias for -x objective-c++-cpp-output

This is the ObjC++ version of r129201. It's for example needed to use
ccache with clang.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@137560 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed