[Driver] Suggest valid integrated tools

Summary:
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

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D42004

llvm-svn: 322517