Support cross linking to arm on ubuntu.

With this patch we correctly determine that ubuntu's ARM tree is not biarch
and use "lib" istead of "lib32".

Without this patch the search inside the arm tree for the crt files was failing
and we would end up trying to use the i686 ones in lib32.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@193528 91177308-0d34-0410-b5e6-96231b3b80d8