[Driver] Do not increment ActionCount for precompiled headers.

[manojgupta]

Summary

If a .h file is specifed as input, it gets compiled to a PCH file.
Handle the PCH Action and do not throw the error:
"cannot specify -o when generating multiple output files"

This fixes PR33533.

[manojgupta]

I am not sure what is the expected behavior. Maybe clang is doing the right thing in rejecting.
But, this creates an issue in ChromeOS land where a package fails to build with clang (https://bugs.chromium.org/p/chromium/issues/detail?id=735206).

lib/Driver/Driver.cpp

 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/raw_ostream.h"
 #include <map>
 #include <memory>
 #include <utility>
 #if LLVM_ON_UNIX
 #include <unistd.h> // getpid
 #endif
+#include <iostream>
 
 using namespace clang::driver;
 using namespace clang;
 using namespace llvm::opt;
 
 Driver::Driver(StringRef ClangExecutable, StringRef DefaultTargetTriple,
                DiagnosticsEngine &Diags,
                IntrusiveRefCntPtr<vfs::FileSystem> VFS)
void Driver::BuildJobs(Compilation &C) const {
 
   Arg *FinalOutput = C.getArgs().getLastArg(options::OPT_o);
 
   // It is an error to provide a -o option if we are making multiple output
   // files.
   if (FinalOutput) {
     unsigned NumOutputs = 0;
     for (const Action *A : C.getActions())
-      if (A->getType() != types::TY_Nothing)
+      if (A->getType() != types::TY_Nothing && A->getType() != types::TY_PCH)
         ++NumOutputs;
 
     if (NumOutputs > 1) {
       Diag(clang::diag::err_drv_output_argument_with_multiple_files);
       FinalOutput = nullptr;
     }
   }