[CUDA] Move AXPY example into gist.

No need to have a long inline code snippet in this doc.

Also move "flags that control numerical code" underneath the "invoking
clang" section, and reformat things a bit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280857 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed