DI/Verifier: Fix argument bitrot in DILocalVariable

Add a verifier check that `DILocalVariable`s of tag
`DW_TAG_arg_variable` always have a non-zero 'arg:' field, and those of
tag `DW_TAG_auto_variable` always have a zero 'arg:' field.  These are
the only configurations that are properly understood by the backend.

(Also, fix the bad examples in LangRef and test/Assembler, and fix the
bug in Kaleidoscope Ch8.)

A large number of testcases seem to have bitrotted their way forward
from some ancient version of the debug info hierarchy that didn't have
`arg:` parameters.  If you have out-of-tree testcases that start failing
in the verifier and you don't care enough to get the `arg:` right, you
may have some luck just calling:

    sed -e 's/, arg: 0/, arg: 1/'

or some such, but I hand-updated the ones in tree.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243183 91177308-0d34-0410-b5e6-96231b3b80d8

examples/Kaleidoscope/Chapter8/toy.cpp

@@ -1255,7 +1255,7 @@ void PrototypeAST::CreateArgumentAllocas(Function *F) {
                                         KSDbgInfo.TheCU->getDirectory());
     DILocalVariable *D = DBuilder->createLocalVariable(
         dwarf::DW_TAG_arg_variable, Scope, Args[Idx], Unit, Line,
-        KSDbgInfo.getDoubleTy(), Idx);
+        KSDbgInfo.getDoubleTy(), true, 0, Idx + 1);
 
     DBuilder->insertDeclare(Alloca, D, DBuilder->createExpression(),
                             DebugLoc::get(Line, 0, Scope),