[PATCH] [FileCheck] Fix a bug that cause FileCheck to misidentify check-prefix

[Tim Northover]

> The current behavior looks like a bug to me, but I'm not
> 100% sure. With this patch, do all the existing tests pass?

I'd agree it's a bug (I hit it myself today, in fact), but haven't you
checked existing tests before committing? If not you should definitely
run "make check-all".

I'm a little concerned about the logic though. Does FileCheck normally
consider A-z and 1-9 as its token range? 1-9 seems particularly odd
(what about 0?) but A-z includes quite a few characters that aren't
usually in tokens too.

Cheers.

Tim.