Add support in the diagnostic verifier for verifying no fix-its

[gregomni]

Checked what it would look like to verify fix-its in every case, and
currently the tests are missing expected fix-its in 435 diagnoses in 60
test files.

So as an alternative, added support for a no fix-its marker “{{}}”, and
added that marker to the c-style for deprecation tests where it applies.

See conversation in #552 for the motivation for this change.

[gribozavr]

I'd prefer something more explicit than {{}} to mean "expect no fix-its", but the direction seems useful to me.

[gregomni]

The text "expected-no-fix-its" is the most explicit way I can think of, but it has the disadvantage of looking like a top-level expected diagnostic instead of a modifier to the previous expected diagnostic. Or make it part of the diagnoses kind, e.g. "expected-warning-no-fix-its"?

As I think of various other possibilities I still like "{{}}". It's in the position of a fix-it, it looks like a fix-it, but it's empty. I think syntactically, it's closest to the intended semantics.

That being said, I'm happy to change to whatever syntax.

[jrose-apple]

:-/ I see why you went with {{}}, but I think I agree with Dmitri that it's not clear enough. I don't really like tacking it on to the "expected" part, though. Some ideas:

• {{none}} - still a little ambiguous if you don't know about fix-it check syntax.
• {{no-fix-its}} - more explicit but starting to get wordy
• Invert the polarity and require {{*}} to ignore fix-its - I don't think this'll fly with the team.

Hm. I don't like any of these.

[lattner]

{{none}} seems servicable to me.

[gregomni]

Alrighty. Switched to {{none}}, committed, squashed.

[jrose-apple]

Other than the one comment issue, this looks good to me!

[gregomni]

Oops! Yep, fixed that.

[gregomni]

(Fixed conflicts with another commit adding warnings for use of ++ to the tests, repushed.)

[jrose-apple]

Thanks, Greg!