[libc++] Exclude posix_l/strtonum fallback inclusion for newlib > 2.4

[rupprecht]

Summary

[libc++] Exclude posix_l/strtonum fallback inclusion for newlib > 2.4

r338122 changed the linkage of some methods which revealed an existing ODR violation, e.g.:

projects/libcxx/include/support/xlocale/__posix_l_fallback.h:83:38: error: 'internal_linkage' attribute does not appear on the first declaration of 'iswcntrl_l'
inline _LIBCPP_INLINE_VISIBILITY int iswcntrl_l(wint_t c, locale_t) {
                                     ^
lib/include/wctype.h:55:12: note: previous definition is here
extern int      iswcntrl_l (wint_t, locale_t);

These were added to newlib in 2.5 [1] [2] (newlib version is 2.4 in the tree when committed), so move them to the already existing include guard.

[1] https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=commit;h=238455adfab4f8070ac65400aac22bb8a9e502fc
[2] https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;a=commit;h=8493c1631643fada62384768408852bc0fa6ff44

[ldionne]

Just to make sure I understand properly: this means we will use newlib's implementation of iswcntrl_l & friends instead of our own emulation (which is an ODR violation currently going unnoticed)? And this is OK because newlib provides iswcntrl_l & friends starting at version 2.4.

This is my understanding. If it is correct, then LGTM.

[jyknight]

Typo in commit message? They were added to 2.5, not 2.4 (the code is right, just the comment is wrong).

[rupprecht]

In D49927#1178659, @ldionne wrote:

Just to make sure I understand properly: this means we will use newlib's implementation of iswcntrl_l & friends instead of our own emulation (which is an ODR violation currently going unnoticed)? And this is OK because newlib provides iswcntrl_l & friends starting at version 2.4.

Yes, that's correct.
I clarified the description: when the methods were added, the tree was configured with NEWLIB_MINOR_VERSION = 4, meaning this wasn't released until the next version, newlib 2.5.

This is my understanding. If it is correct, then LGTM.

include/support/newlib/xlocale.h

 
 #include <cstdlib>
 #include <clocale>
 #include <cwctype>
 #include <ctype.h>
 #if !defined(__NEWLIB__) || __NEWLIB__ < 2 || \
     __NEWLIB__ == 2 && __NEWLIB_MINOR__ < 5
 #include <support/xlocale/__nop_locale_mgmt.h>
-#endif
 #include <support/xlocale/__posix_l_fallback.h>
 #include <support/xlocale/__strtonum_fallback.h>
+#endif
 
 #endif // _NEWLIB_VERSION
 
 #endif