[CUDA] Add section to docs about controlling fp optimizations.

Reviewers: rnk

Subscribers: llvm-commits, tra

Differential Revision: http://reviews.llvm.org/D20494

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270789 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed