DebugInfo: Add metadata support for disabling DWARF pub sections

In cases where the debugger load time is a worthwhile tradeoff (or less
costly - such as loading from a DWP instead of a variety of DWOs
(possibly over a high-latency/distributed filesystem)) against object
file size, it can be reasonable to disable pubnames and corresponding
gdb-index creation in the linker.

A backend-flag version of this was implemented for NVPTX in
D44385/r327994 - which was fine for NVPTX which wouldn't mix-and-match
CUs. Now that it's going to be a user-facing option (likely powered by
"-gno-pubnames", the same as GCC) it should be encoded in the
DICompileUnit so it can vary per-CU.

After this, likely the NVPTX support should be migrated to the metadata
& the previous flag implementation should be removed.

Reviewers: aprantl

Differential Revision: https://reviews.llvm.org/D50213

llvm-svn: 339939

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -1603,7 +1603,7 @@ void ModuleBitcodeWriter::writeDICompileUnit(const DICompileUnit *N,
   Record.push_back(VE.getMetadataOrNullID(N->getMacros().get()));
   Record.push_back(N->getSplitDebugInlining());
   Record.push_back(N->getDebugInfoForProfiling());
-  Record.push_back(N->getGnuPubnames());
+  Record.push_back((unsigned)N->getNameTableKind());
 
   Stream.EmitRecord(bitc::METADATA_COMPILE_UNIT, Record, Abbrev);
   Record.clear();