Add a debug info code generation level to the compile unit metadata

and update everything accordingly. This can be used to conditionalize
the amount of output in the backend based on the amount of debug
requested/metadata emission scheme by a front end (e.g. clang).

Paired with a commit to clang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202332 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/DebugInfo.h

@@ -427,6 +427,7 @@ public:
   DIArray getImportedEntities() const;
 
   StringRef getSplitDebugFilename() const { return getStringField(12); }
+  unsigned getEmissionKind() const { return getUnsignedField(13); }
 
   /// Verify - Verify that a compile unit is well formed.
   bool Verify() const;