locale.c: Remove use of nl_langinfo_l()

I was wrong that it was feasible to determine at Configure time if this
was a thread safe implementation or not.  What could be determined was
if it was obviously not thread-safe.  lThe major advantage of using
this, is hence not valid, so remove the code that handled it specially.

perl.h comments are updated

locale.c

@@ -4694,37 +4694,10 @@ S_my_langinfo_i(pTHX_
  * implementation doesn't currently worry about it.  But it is a problem on
  * Windows boxes, which don't have nl_langinfo(). */
 
-#  if defined(HAS_THREAD_SAFE_NL_LANGINFO_L) && defined(USE_POSIX_2008_LOCALE)
-
-    /* Simplest is if we can use nl_langinfo_l()
-     *
-     * With it, we can change LC_CTYPE in the same call as the other category */
-#    ifdef USE_LOCALE_CTYPE
-#      define CTYPE_SAFETY_MASK LC_CTYPE_MASK
-#    else
-#      define CTYPE_SAFETY_MASK 0
-#    endif
-
-    locale_t cur = newlocale((category_masks[cat_index] | CTYPE_SAFETY_MASK),
-                             locale, (locale_t) 0);
-
-    retval = save_to_buffer(nl_langinfo_l(item, cur), retbufp, retbuf_sizep);
-
-    if (utf8ness) {
-        *utf8ness = get_locale_string_utf8ness_i(retval,
-                                                 LOCALE_UTF8NESS_UNKNOWN,
-                                                 locale, cat_index);
-    }
-
-    freelocale(cur);
-
-    return retval;
 /*--------------------------------------------------------------------------*/
-#  elif defined(HAS_NL_LANGINFO) /* nl_langinfo() is available.  */
+#  if defined(HAS_NL_LANGINFO) /* nl_langinfo() is available.  */
 
-    /* The second version of my_langinfo() is if we have plain nl_langinfo()
-     *
-     * The only difference between the normal and emulation is the type of
+    /* The only difference between the normal and emulation is the type of
      * locks.  We have to always lock because this nl_langinfo() isn't thread
      * safe  */
 #    ifndef USE_THREAD_SAFE_LOCALE_EMULATION

perl.h

@@ -1365,20 +1365,22 @@ violations are fatal.
 
 #  include "perl_langinfo.h"    /* Needed for _NL_LOCALE_NAME */
 
-/* Allow use of glibc's undocumented querylocale() equivalent if asked for, and
- * appropriate */
 #  ifdef USE_POSIX_2008_LOCALE
 #    if  defined(HAS_QUERYLOCALE)                                           \
-              /* Has this internal undocumented item for nl_langinfo() */   \
+              /* Use querylocale if has it, or has the glibc internal       \
+               * undocumented equivalent. */                                \
      || (     defined(_NL_LOCALE_NAME)                                      \
-              /* And asked for */                                           \
+              /* And is asked for */                                        \
          &&   defined(USE_NL_LOCALE_NAME)                                   \
-              /* We need the below because we will be calling it within a   \
-               * macro, can't have it get messed up by another thread. */   \
-         &&   defined(HAS_THREAD_SAFE_NL_LANGINFO_L)                        \
+              /* nl_langinfo_l almost certainly will exist on systems that  \
+               * have _NL_LOCALE_NAME, so there is nothing lost by          \
+               * requiring it instead of also allowing plain nl_langinfo(). \
+               * And experience indicates that its glibc implementation is  \
+               * thread-safe, eliminating code complications */             \
+         &&   defined(HAS_NL_LANGINFO_L)                                    \
                /* On systems that accept any locale name, the real          \
                 * underlying locale is often returned by this internal      \
-                * item, so we can't use it */                               \
+                * langinfo item, so we can't use it */                      \
          && ! defined(SETLOCALE_ACCEPTS_ANY_LOCALE_NAME))
 #      define USE_QUERYLOCALE
 #    endif