[XRay][compiler-rt] Add another work-around to XRay FDR tests when TSC emulation is needed

This patch applies a work-around to the XRay FDR tests when TSC emulation is 
needed because the processor frequency cannot be determined.

This fixes PR32620 using the suggestion given by Dean in comment 1.

Reviewers: dberris

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31967

llvm-svn: 300017