[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

   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) {