[CMake] Add mapping for IBM XL -qnoeh and -qnortti

Summary:
This patch maps in the `-qnoeh` and `-qnortti` options for building with
IBM XL compilers.

Reviewers: daltenty, xingxue, jasonliu

Reviewed By: daltenty

Subscribers: mgorny, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65669

llvm-svn: 368050