[GlobalISel] Get the AArch64 tests to work on Linux

Mostly this just means changing the triple from aarch64-apple-ios to the generic
aarch64--. Only one test needs more significant changes, but GlobalISel already
does the right thing so it's ok to just change the checks.

Differential Revision: https://reviews.llvm.org/D25532

llvm-svn: 284223