[driver] In general, the driver claims redundant args and uses the last arg.

However, the '-x' option has special handling and wasn't following this
paradigm.  Fix it to do so by claiming the arg as we parse the '-x' option.
rdar://11203340

llvm-svn: 154231

clang/lib/Driver/Driver.cpp

@@ -1003,6 +1003,7 @@ void Driver::BuildInputs(const ToolChain &TC, const DerivedArgList &Args,
     } else if (A->getOption().matches(options::OPT_x)) {
       InputTypeArg = A;
       InputType = types::lookupTypeForTypeSpecifier(A->getValue(Args));
+      A->claim();
 
       // Follow gcc behavior and treat as linker input for invalid -x
       // options. Its not clear why we shouldn't just revert to unknown; but

clang/test/Driver/redundant-args.c

@@ -0,0 +1,2 @@
+// RUN: %clang -target x86_64-apple-darwin10 \
+// RUN:   -Werror -x c -x c -fsyntax-only %s