Revert "[clang][driver] Emit a warning if -xc/-xc++ is after the last input file"

This reverts commit 1c1a4b9.

Some builders failed.

Author: kongy

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -365,9 +365,6 @@ def warn_drv_preprocessed_input_file_unused : Warning<
 def warn_drv_unused_argument : Warning<
   "argument unused during compilation: '%0'">,
   InGroup<UnusedCommandLineArgument>;
-def warn_drv_unused_x : Warning<
-  "‘-x %0’ after last input file has no effect">,
-  InGroup<UnusedCommandLineArgument>;
 def warn_drv_empty_joined_argument : Warning<
   "joined argument expects additional value: '%0'">,
   InGroup<UnusedCommandLineArgument>;

clang/lib/Driver/Driver.cpp

@@ -2308,15 +2308,6 @@ void Driver::BuildInputs(const ToolChain &TC, DerivedArgList &Args,
     assert(!Args.hasArg(options::OPT_x) && "-x and /TC or /TP is not allowed");
   }
 
-  // Warn -x after last input file has no effect
-  {
-    Arg *LastXArg = Args.getLastArgNoClaim(options::OPT_x);
-    Arg *LastInputArg = Args.getLastArgNoClaim(options::OPT_INPUT);
-    if (LastInputArg->getIndex() < LastXArg->getIndex()) {
-      Diag(clang::diag::warn_drv_unused_x) << LastXArg->getValue();
-    }
-  }
-
   for (Arg *A : Args) {
     if (A->getOption().getKind() == Option::InputClass) {
       const char *Value = A->getValue();