Created attachment 6449 [details]
Potential fix

newlocale() neglects to set errno to an appropriate value when failing, if it
has already been asked about the same incorrect locale name.

#include <stdio.h>
#include <errno.h>
#include <locale.h>

int
main(int argc, char **argv)
{
  locale_t loc;

  setlocale(LC_ALL, "C");

  errno = 0;
  loc = newlocale(LC_COLLATE_MASK | LC_CTYPE_MASK,
          "nb_no.utf8",
          0);
  printf("result = %p errno = %d\n", loc, errno);

  errno = 0;
  loc = newlocale(LC_COLLATE_MASK | LC_CTYPE_MASK,
          "nb_no.utf8",
          0);
  printf("result = %p errno = %d\n", loc, errno);

  return 0;
}


Actual results:
result = (nil) errno = 2
result = (nil) errno = 0

Expected results:
result = (nil) errno = 2
result = (nil) errno = 2     (or at least something other than 0)