[Driver] Suggest valid integrated tools
There are only two valid integrated Clang driver tools: -cc1 and
-cc1as. If a user asks for an unknown tool, such as -cc1asphalt,
an error message is displayed to indicate that there is no such tool,
but the message doesn't indicate what the valid options are.
Include the valid options in the error message.
Test Plan: check-clang
Reviewers: sepavloff, bkramer, phosek
Reviewed By: bkramer
Differential Revision: https://reviews.llvm.org/D42004