Fix go bindings test when using goma distributed build tool

Goma[1] is a distributed build system similar to distcc and icecc
primarily used to compile Chromium. The client is open source, and
hopefully soon the server will be as well. The intended usage model is
similar to most distributed build systems: prefix gomacc onto your
compiler command line, and it transparently distributes compilation.

The go lit config wants to determine the host compiler binary, so it
needs some extra logic to avoid looking at these prefixes.

[1] https://chromium.googlesource.com/infra/goma/client/

llvm-svn: 328580