[CF] DT_WHT is unavailable on OpenBSD.

[3405691582]

Here we duplicate this extended conditional to not reference DT_WHT,
which is not available on OpenBSD. It is probably harmless to actually
remove DT_WHT entirely here unconditionally, but would require grokking
more context for a simple buildfix.

It also seems more readable to duplicate the entire line in the ifdef
despite being able to squish the ifdef in the clause.

[3405691582]

Let me know if you'd prefer adding some additional preprocessor symbols in (maybe) CoreFoundation_Prefix.h instead of injecting actual OS preprocessor symbols.

[parkera]

Is TARGET_OS_BSD from TargetConditionals.h not appropriate?

[3405691582]

DT_WHT is available on FreeBSD (source) and NetBSD (source), but not OpenBSD (source), so TARGET_OS_BSD on its own is too broad here.

(I'm also wondering what the ideal stylistic choice is for future PRs as well; for example, Linux doesn't have xlocale, FreeBSD does, but the other BSDs do not...)

[3405691582]

Perhaps it's better stylistically to leave granular portability decisions to CoreFoundation_Prefix.h: so, for this example,

#if TARGET_OS_BSD && defined(__OpenBSD__)
#define __HAS_DT_WHT__ 1
#else
#define __HAS_DT_WHT__ 0
#endif  

and then use __HAS_DT_WHT__ in CFFileUtilities instead? This means macros in the dependent files are focused on features as opposed to operating systems. It does make the prefix file a lot more verbose though (but on the other hand it's already rather verbose to begin with), and can lead to some twisty and/or lengthy preprocessor conditionals...

[parkera]

I tried that approach in the past (focus on features instead of platforms) but was never happy with the result. It just results in a lot of extra macros, most of which are just aliases for "platform X".

[3405691582]

Sounds good. I'll keep this commit as-is and use that pattern for future PRs.

[compnerd]

@swift-ci please test

[compnerd]

I wish that there was a better way to write this, but I suppose it will do for now.

[3405691582]

It'll possibly look better if refactored slightly, but I'll think about circling back around to that after I'm done with all the portability tweaks.