Simplify CMake rules in HandleLLVMOptions module.

Summary: No functionality change.

Reviewers: Bigcheese

Reviewed By: Bigcheese

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D535

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176973 91177308-0d34-0410-b5e6-96231b3b80d8