[XRay] ARM 32-bit no-Thumb support in LLVM

This is a port of XRay to ARM 32-bit, without Thumb support yet. The XRay instrumentation support is moving up to AsmPrinter.
This is one of 3 commits to different repositories of XRay ARM port. The other 2 are:

1. https://reviews.llvm.org/D23932 (Clang test)
2. https://reviews.llvm.org/D23933 (compiler-rt)

Differential Revision: https://reviews.llvm.org/D23931

llvm-svn: 280888