Specify non-GNU-ARM triples for key-function test.

Since ARM has diverging ABIs on this detail, it's probably worth
testing both it and a "normal" Itanium system.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@173576 91177308-0d34-0410-b5e6-96231b3b80d8