Fix the MS-Windows build as followup to Gnulib regex import

* lib-src/ntlib.c (nl_langinfo): New function.  (Bug#32194)

lib-src/ntlib.c

@@ -31,6 +31,10 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <ctype.h>
 #include <sys/timeb.h>
 #include <mbstring.h>
+#include <locale.h>
+
+#include <nl_types.h>
+#include <langinfo.h>
 
 #include "ntlib.h"
 
@@ -423,3 +427,66 @@ sys_open (const char * path, int oflag, int mode)
 {
   return _open (path, oflag, mode);
 }
+
+/* Emulation of nl_langinfo that supports only CODESET.
+   Used in Gnulib regex.c.  */
+char *
+nl_langinfo (nl_item item)
+{
+  switch (item)
+    {
+      case CODESET:
+	{
+	  /* Shamelessly stolen from Gnulib's nl_langinfo.c, modulo
+	     CPP directives.  */
+	  static char buf[2 + 10 + 1];
+	  char const *locale = setlocale (LC_CTYPE, NULL);
+	  char *codeset = buf;
+	  size_t codesetlen;
+	  codeset[0] = '\0';
+
+	  if (locale && locale[0])
+	    {
+	      /* If the locale name contains an encoding after the
+		 dot, return it.  */
+	      char *dot = strchr (locale, '.');
+
+	      if (dot)
+		{
+		  /* Look for the possible @... trailer and remove it,
+		     if any.  */
+		  char *codeset_start = dot + 1;
+		  char const *modifier = strchr (codeset_start, '@');
+
+		  if (! modifier)
+		    codeset = codeset_start;
+		  else
+		    {
+		      codesetlen = modifier - codeset_start;
+		      if (codesetlen < sizeof buf)
+			{
+			  codeset = memcpy (buf, codeset_start, codesetlen);
+			  codeset[codesetlen] = '\0';
+			}
+		    }
+		}
+	    }
+	  /* If setlocale is successful, it returns the number of the
+	     codepage, as a string.  Otherwise, fall back on Windows
+	     API GetACP, which returns the locale's codepage as a
+	     number (although this doesn't change according to what
+	     the 'setlocale' call specified).  Either way, prepend
+	     "CP" to make it a valid codeset name.  */
+	  codesetlen = strlen (codeset);
+	  if (0 < codesetlen && codesetlen < sizeof buf - 2)
+	    memmove (buf + 2, codeset, codesetlen + 1);
+	  else
+	    sprintf (buf + 2, "%u", GetACP ());
+	  codeset = memcpy (buf, "CP", 2);
+
+	  return codeset;
+	}
+      default:
+	return (char *) "";
+    }
+}