bug in strcasecmp and strncasecmp

[Bruno Haible]

Per POSIX [1], the functions strcasecmp and strncasecmp should
"use the current locale to determine the case of the characters.".

[1] https://pubs.opengroup.org/onlinepubs/9799919799/functions/strcasecmp.html

This is not what Cygwin does: In the fr_FR.ISO8859-1 locale, the
characters 0xE9 and 0xC9 are the same modulo case, but strcasecmp
and strncasecmp consider these characters to be different.

How to reproduce (in Cygwin 2.9.0 or 3.5.6):
============================= foo.c ==========================
#include <stdio.h>
#include <ctype.h>
#include <locale.h>
#include <strings.h>

int main ()
{
  if (setlocale (LC_ALL, "fr_FR.ISO8859-1") == NULL)
    return 1;
  int c1 = (unsigned char) '\311';
  int c2 = (unsigned char) '\351';

  printf ("0x%02X -> 0x%02X, 0x%02X\n", c1, tolower (c1), toupper (c1));
  printf ("0x%02X -> 0x%02X, 0x%02X\n", c2, tolower (c2), toupper (c2));
  printf ("strcasecmp  -> %d\n", strcasecmp ("Fej\311r", "Fej\351r"));
  printf ("strncasecmp -> %d\n", strncasecmp ("Fej\311r", "Fej\351r", 5));
}
=======================================================================
$ gcc -Wall foo.c
$ ./a

Expected output:
0xC9 -> 0xE9, 0xC9
0xE9 -> 0xE9, 0xC9
strcasecmp  -> 0
strncasecmp -> 0

Actual output:
0xC9 -> 0xE9, 0xC9
0xE9 -> 0xE9, 0xC9
strcasecmp  -> 256
strncasecmp -> 256

Bruno