[NVPTX] Initial adaptation of MCAsmStreamer/MCTargetStreamer for debug info in Cuda.
Summary:
Initial changes in interfaces of MCAsmStreamer/MCTargetStreamer for
correct debug info emission for Cuda.
1. PTX foramt does not support `.ascii` directives. Added the ability to
nullify it.
2. The initial function label must follow the first debug `.loc`
directive, not be followed by.
3. DWARF sections must be enclosed in braces.
Reviewers: hfinkel, probinson, jlebar, rafael, echristo
Subscribers: sdardis, nemanjai, llvm-commits, aprantl
Differential Revision: https://reviews.llvm.org/D40033
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321178
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