DebugInfo: Gut DISubprogram and DILexicalBlock*

Gut the `DIDescriptor` wrappers around `MDLocalScope` subclasses.  Note
that `DILexicalBlock` wraps `MDLexicalBlockBase`, not `MDLexicalBlock`.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234850 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Verifier.cpp

@@ -991,7 +991,7 @@ void Verifier::visitMDSubprogram(const MDSubprogram &N) {
         continue;
 
       // FIXME: Once N is canonical, check "SP == &N".
-      Assert(DISubprogram(SP).describes(F),
+      Assert(SP->describes(F),
              "!dbg attachment points at wrong subprogram for function", &N, F,
              &I, DL, Scope, SP);
     }