Forced crash under macOS 14 due to internal threading

[Tom]

Running the following:

```
#include <libintl.h>
#include <stdlib.h>
#include <unistd.h>

int main() {
  unsetenv("LANG");

  setlocale(LC_ALL, "");

  if (fork() == 0) {
    gettext("test");
  }
}
```

under macos14, crashes with the following error:

```
objc[16942]: +[__SwiftNativeNSStringBase initialize] may have been in progress 
in another thread when fork() was called.
objc[16942]: +[__SwiftNativeNSStringBase initialize] may have been in progress 
in another thread when fork() was called. We cannot safely call it or ignore it 
in the fork() child process. Crashing instead. Set a breakpoint on 
objc_initializeAfterForkError to debug.
```

The call to `setlocale` spawns threads (via `dispatch_apply`) with the 
following backtrace:

```
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
  * frame #0: 0x0000000182c5602c libdispatch.dylib`dispatch_apply
    frame #1: 0x0000000183000af0 CoreFoundation`__103-[CFPrefsSearchListSource 
synchronouslySendSystemMessage:andUserMessage:andDirectMessage:replyHandler:]_block_invoke.52
 + 132
    frame #2: 0x0000000182e86cbc 
CoreFoundation`CFPREFERENCES_IS_WAITING_FOR_SYSTEM_AND_USER_CFPREFSDS + 100
    frame #3: 0x0000000182fffce0 CoreFoundation`-[CFPrefsSearchListSource 
synchronouslySendSystemMessage:andUserMessage:andDirectMessage:replyHandler:] + 
232
    frame #4: 0x0000000182e84f68 CoreFoundation`-[CFPrefsSearchListSource 
alreadylocked_generationCountFromListOfSources:count:] + 232
    frame #5: 0x0000000182e84c70 CoreFoundation`-[CFPrefsSearchListSource 
alreadylocked_getDictionary:] + 492
    frame #6: 0x0000000182e847dc CoreFoundation`-[CFPrefsSearchListSource 
alreadylocked_copyValueForKey:] + 172
    frame #7: 0x0000000182e84710 CoreFoundation`-[CFPrefsSource 
copyValueForKey:] + 52
    frame #8: 0x0000000182e846c4 CoreFoundation`__76-[_CFXPreferences 
copyAppValueForKey:identifier:container:configurationURL:]_block_invoke + 32
    frame #9: 0x0000000182e7dd00 
CoreFoundation`__108-[_CFXPreferences(SearchListAdditions) 
withSearchListForIdentifier:container:cloudConfigurationURL:perform:]_block_invoke
 + 376
    frame #10: 0x00000001830013a0 CoreFoundation`-[_CFXPreferences 
withSearchListForIdentifier:container:cloudConfigurationURL:perform:] + 384
    frame #11: 0x0000000182e7d5d8 CoreFoundation`-[_CFXPreferences 
copyAppValueForKey:identifier:container:configurationURL:] + 156
    frame #12: 0x0000000182e7d500 
CoreFoundation`_CFPreferencesCopyAppValueWithContainerAndConfiguration + 112
    frame #13: 0x00000001004827e4 libintl.8.dylib`_libintl_locale_name_default 
+ 72
    frame #14: 0x0000000100481990 libintl.8.dylib`libintl_setlocale + 164
    frame #15: 0x0000000100003f38 main`main + 52
    frame #16: 0x0000000182a6a0e0 dyld`start + 2360
```

and the call to `gettext` triggers this crash (via 
`performForkChildInitialize`) with the following backtrace:

```
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
  * frame #0: 0x0000000182a382c4 libobjc.A.dylib`objc_initializeAfterForkError
    frame #1: 0x0000000182a38448 
libobjc.A.dylib`performForkChildInitialize(objc_class*, objc_class*) + 376
    frame #2: 0x0000000182a1eba4 libobjc.A.dylib`initializeNonMetaClass + 572
    frame #3: 0x0000000182a1ea04 libobjc.A.dylib`initializeNonMetaClass + 156
    frame #4: 0x0000000182a1ea04 libobjc.A.dylib`initializeNonMetaClass + 156
    frame #5: 0x0000000182a3bbfc 
libobjc.A.dylib`initializeAndMaybeRelock(objc_class*, objc_object*, 
locker_mixin<lockdebug::lock_mixin<objc_lock_base_t>>&, bool) + 164
    frame #6: 0x0000000182a1e5c4 libobjc.A.dylib`lookUpImpOrForward + 892
    frame #7: 0x0000000182a1df64 libobjc.A.dylib`_objc_msgSend_uncached + 68
    frame #8: 0x0000000192dfbbc8 libswiftCore.dylib`type metadata accessor for 
Swift.__StringStorage + 24
    frame #9: 0x0000000192b85f24 
libswiftCore.dylib`Swift.String._bridgeToObjectiveCImpl() -> Swift.AnyObject + 
152
    frame #10: 0x0000000184409f80 Foundation`function signature specialization 
<Arg[1] = Dead> of Foundation.LocaleCache.preferredLanguages(forCurrentUser: 
Swift.Bool) -> Swift.Array<Swift.String> + 76
    frame #11: 0x00000001844ec9c4 Foundation`@objc static 
__C.NSLocale._preferredLanguagesForCurrentUser(Swift.Bool) -> 
Swift.Array<Swift.String> + 44
    frame #12: 0x0000000182ece0b4 CoreFoundation`CFLocaleCopyPreferredLanguages 
+ 28
    frame #13: 0x0000000100a553dc 
libintl.8.dylib`_libintl_language_preferences_default + 68
    frame #14: 0x0000000100a53d40 libintl.8.dylib`libintl_dcigettext + 812
    frame #15: 0x00000001005d7f10 main`main + 120
    frame #16: 0x0000000182a6a0e0 dyld`start + 2360
```

This is the case with `gettext` 0.22.5, 0.21.1 and 0.20.2; 0.19.8.1 does not 
exhibit this behaviour as it doesn't call `CFLocaleCopyPreferredLanguages`.

Regards,
Tom