[DebugInfo] Use DbgVariableIntrinsic as the base class of variables.

[HsiangKai]

Summary

After refactoring DbgInfoIntrinsic class hierarchy, we use
DbgVariableIntrinsic as the base class of variable debug info.

In resolveTopLevelMetadata() in CGVTables.cpp, we only care about
dbg.value, so we try to cast the instructions to DbgVariableIntrinsic
before resolving variables.

lib/CodeGen/CGVTables.cpp

if (!DIS)
     return;
   auto *NewDIS = DIS->replaceWithDistinct(DIS->clone());
   VMap.MD()[DIS].reset(NewDIS);
 
   // Find all llvm.dbg.declare intrinsics and resolve the DILocalVariable nodes
   // they are referencing.
   for (auto &BB : Fn->getBasicBlockList()) {
     for (auto &I : BB) {
-      if (auto *DII = dyn_cast<llvm::DbgInfoIntrinsic>(&I)) {
+      if (auto *DII = dyn_cast<llvm::DbgVariableIntrinsic>(&I)) {
         auto *DILocal = DII->getVariable();
         if (!DILocal->isResolved())
           DILocal->resolve();
       }
     }
   }
 }