[tlbuild] casefolding fallback search

[Hironobu Yamashita]

Hi Mojca,

> Any version of Mac OS X / macOS can have the hard drive formatted as
> either case sensitive or case insensitive. Nothing changed with 10.13.
> Yes, the default file system changed, but one can still format the
> drive as either case sensitive or case insensitive.

Thanks for your explanation.

> I have absolutely no idea how the patch could or should(?) affect
> macOS, but it should certainly not be "#ifdef __APPLE" or anything in
> that sense because the functionality depends on the way the disk has
> been formatted.

Agreed. Maybe only skipping --(no-)casefold-search test on macOS is
enough, as we cannot assume whether the file system is
case-sensitive or not.

Hironobu