[OpenCL] Extended mapping of parcing CodeGen arguments

Summary: Enable cl_mad_enamle and cl_no_signed_zeros options when user turns on cl_unsafe_math_optimizations or cl_fast_relaxed_math options.

Reviewers: Anastasia, cfe-commits

Reviewed By: Anastasia

Subscribers: bader, yaxunl

Differential Revision: https://reviews.llvm.org/D31324

llvm-svn: 298838