[XRay] Check in Clang whether XRay supports the target when -fxray-instrument is passed

Added the code which explicitly emits an error in Clang in case
`-fxray-instrument` is passed, but XRay is not supported for the
selected target.

Author: rSerge

Reviewers: dberris, rsmith, aaron.ballman, rnk

Subscribers: cfe-commits, iid_iunknown

Differential Revision: https://reviews.llvm.org/D24799

llvm-svn: 283193