Replace getAs/dyn_cast with castAs/cast to fix null dereference static analyzer warnings.

Both these casts are immediately deferenced and the cast will assert for us that they are of the correct type.

Author: RKSimon

clang/lib/Frontend/Rewrite/RewriteModernObjC.cpp

@@ -2688,7 +2688,7 @@ Stmt *RewriteModernObjC::RewriteObjCBoxedExpr(ObjCBoxedExpr *Exp) {
   // Don't forget the parens to enforce the proper binding.
   ParenExpr *PE = new (Context) ParenExpr(StartLoc, EndLoc, cast);
 
-  const FunctionType *FT = msgSendType->getAs<FunctionType>();
+  auto *FT = msgSendType->castAs<FunctionType>();
   CallExpr *CE = CallExpr::Create(*Context, PE, MsgExprs, FT->getReturnType(),
                                   VK_RValue, EndLoc);
   ReplaceStmt(Exp, CE);
@@ -7501,8 +7501,7 @@ Stmt *RewriteModernObjC::RewriteObjCIvarRefExpr(ObjCIvarRefExpr *IV) {
         RD = RD->getDefinition();
         if (RD && !RD->getDeclName().getAsIdentifierInfo()) {
           // decltype(((Foo_IMPL*)0)->bar) *
-          ObjCContainerDecl *CDecl =
-            dyn_cast<ObjCContainerDecl>(D->getDeclContext());
+          auto *CDecl = cast<ObjCContainerDecl>(D->getDeclContext());
           // ivar in class extensions requires special treatment.
           if (ObjCCategoryDecl *CatDecl = dyn_cast<ObjCCategoryDecl>(CDecl))
             CDecl = CatDecl->getClassInterface();