[XRay][compiler-rt] Add support for TSC emulation for x86_64 to xray_fdr_logging.cc

Previously in r297800, a work-around was created to use TSC emulation on x86_64 when RDTSCP was not available on the host. A similar change was needed in the file xray_fdr_logging.cc which this patch ports over to that file.

Eventually the code should be refactored as there will be 3 locations with the same code, but that can be done as a separate step. This patch is just to keep the test from failing on my machine due to an illegal instruction since RDTSCP is not available on my x86_64 linux VM.

Reviewers: dberris

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31909

llvm-svn: 299922