[NFC][CLANG] Fix Static Code Analyzer Concerns

[Manna]

Summary

This patch uses castAs instead of getAs which will assert if the type doesn't match to resolve dereference issue with nullptr FPT when calling getThisType() in clang::​CodeGen::​CGDebugInfo::​CreateType(clang::​MemberPointerType const *, llvm::​DIFile *).

[Manna]

Thank you @erichkeane for reviews!

clang/lib/CodeGen/CGDebugInfo.cpp

llvm::DIType *CGDebugInfo::CreateType(const MemberPointerType *Ty,
 
   llvm::DIType *ClassType = getOrCreateType(QualType(Ty->getClass(), 0), U);
   if (Ty->isMemberDataPointerType())
     return DBuilder.createMemberPointerType(
         getOrCreateType(Ty->getPointeeType(), U), ClassType, Size, /*Align=*/0,
         Flags);
 
   const FunctionProtoType *FPT =
-      Ty->getPointeeType()->getAs<FunctionProtoType>();
+      Ty->getPointeeType()->castAs<FunctionProtoType>();
   return DBuilder.createMemberPointerType(
       getOrCreateInstanceMethodType(
           CXXMethodDecl::getThisType(FPT, Ty->getMostRecentCXXRecordDecl()),
           FPT, U),
       ClassType, Size, /*Align=*/0, Flags);
 }
 
 llvm::DIType *CGDebugInfo::CreateType(const AtomicType *Ty, llvm::DIFile *U) {