Debian multiarch additionally adds /usr/include/<triplet> and somehow
Android borrowed the idea. (Note /usr/<triplet>/include is already an
include dir...). On Debian, we should just assume a GCC installation is
available and use its triple.
This improves the coverage for the multilib directories used for ARM. Also add
tests covering the internal triple (thumbv7-*). The Juno board can be run in
this configuration.
llvm-svn: 255328