ARM: keep special non-AEABIness of "-darwin-eabi" triples for now

Longer term, we want to move users to "*-*-*-macho" for embedded work, but for
now people are relying on the last thing we told them, which is unfortunately
"*-*-darwin-eabi".

rdar://problem/15703934

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198602 91177308-0d34-0410-b5e6-96231b3b80d8