NFC, make XFAIL work on macOS correctly for test/Driver/XRay/xray-instrument-os.c

The test 'test/Driver/XRay/xray-instrument-os.c' is supposed to XFAIL on -darwin triples.
However, LLVM can be configured to be built with a -macos triple instead, which is equivalent
to -darwin. This commit updates the XFAIL condition to also XFAIL with a -macos host triple.

llvm-svn: 360374