[DEBUGINFO, NVPTX]DO not emit ',debug' option if no debug info or only debug...

[DEBUGINFO, NVPTX]DO not emit ',debug' option if no debug info or only debug directives are requested.

Summary:
If the output of debug directives only is requested, we should drop
emission of ',debug' option from the target directive. Required for
supporting of nvprof profiler.

Reviewers: probinson, echristo, dblaikie

Subscribers: Hahnfeld, jholewinski, llvm-commits, JDevlieghere, aprantl

Differential Revision: https://reviews.llvm.org/D46061

llvm-svn: 345972