Add ARM test for r227489, but XFAIL because this is actually more work than it appeared to be.

Also revert r227489 since it didn't actually fix the thing I thought I
was fixing (since the test case was targeting the wrong architecture
initially). The change might be correct & demonstrated by other test
cases, but it's not a priority for me to find those test cases right
now.

Filed PR22417 for the failure.

llvm-svn: 227632