[XRay][AArch64] An attempt to fix test patching-unpatching.cc by flushing the...

[XRay][AArch64] An attempt to fix test patching-unpatching.cc by flushing the instruction cache after code modification

Summary: This patch attempts to fix test patching-unpatching.cc . The new code flushes the instruction cache after modifying the program at runtime.

Reviewers: dberris, rengolin

Subscribers: llvm-commits, iid_iunknown, aemerson

Differential Revision: https://reviews.llvm.org/D27996

llvm-svn: 290354