Fix non-portable GNU diff option

Summary: This is a fix to revision D68839 and rL375023. This patch substitutes POSIX option "-b" for the non-portable GNU option "--strip-trailing-cr".

Reviewers: daltenty, hubert.reinterpretcast

Reviewed By: daltenty

Subscribers: mehdi_amini, hiraditya, steven_wu, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69342