[clang][tooling] Allow -cc1 arguments in ToolInvocation

ToolInvocation is useful even if you already have a -cc1 invocation,
since it provides a standard way to setup diagnostics, parse arguments,
and handoff to a ToolAction. So teach it to support -cc1 commands by
skipping the driver bits.

Differential Revision: https://reviews.llvm.org/D132615