[XRay][Arm] Enable back XRay testing on Arm32 and fix the failing tests

Summary:
Testing of XRay was occasionally disabled on 32-bit Arm targets (someone assumed that XRay was supported on 64-bit targets only). This patch should fix that problem. Also here the instruction&data cache incoherency problem is fixed, because it may be causing a test to fail.
This patch is one of a series: see also
- https://reviews.llvm.org/D28624

Reviewers: dberris, rengolin

Reviewed By: rengolin

Subscribers: llvm-commits, aemerson, rengolin, dberris, iid_iunknown

Differential Revision: https://reviews.llvm.org/D28623

llvm-svn: 292211