DebugInfo: Implement MDLocation::getInlinedAtScope()

Write `MDLocation::getInlinedAtScope()` and use it to re-implement
`DebugLoc::getScopeNode()` (and simplify `DISubprogram::Verify()`).
This follows the inlined-at linked list and returns the scope of the
deepest/last location.

llvm-svn: 233568
diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index ec4f95e..e16ac8c 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -349,9 +349,7 @@
           continue;
 
         // walk the inlined-at scopes
-        while (MDLocation *IA = DL->getInlinedAt())
-          DL = IA;
-        MDScope *Scope = DL->getScope();
+        MDScope *Scope = DL->getInlinedAtScope();
         if (!Scope)
           return false;
         while (!isa<MDSubprogram>(Scope)) {