IR: Add missing tests for function-local metadata

Add assembly and bitcode tests that I neglected to add in r223564 (IR:
Disallow complicated function-local metadata) and r223574 (IR: Disallow
function-local metadata attachments).

Found a couple of bugs:

  - The error message for function-local attachments gave the wrong line
    number -- it indicated the next token (typically on the next line)
    instead of the token that started the attachment.  Fixed.

  - Metadata arguments of the form `!{i32 0, i32 %v}` (or with the
    arguments reversed) fired an assertion in `ValueEnumerator` in LLVM
    v3.5, so I suppose this never really worked.  I suppose this was
    "fixed" by r223564.

(Thanks to dblaikie for pointing out my omission.)

Part of PR21532.