unistd: guarantee STDIN_FILENO here, for OS/2 EMX * lib/unistd.in.h (STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO): Guarantee a definition. * doc/posix-headers/unistd.texi (unistd.h): Document the bug. * modules/unistd-safer (Depends-on): Add dependency on unistd. * lib/c-stack.c (STDERR_FILENO): Rely on <unistd.h>. * lib/dup-safer.c (STDERR_FILENO): Likewise. * lib/execute.c (STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO): Likewise. * lib/fd-safer.c (STDIN_FILENO, STDERR_FILENO): Likewise. * lib/fopen-safer.c (STDERR_FILENO): Likewise. * lib/pipe.c (STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO): Likewise. * lib/tmpfile-safer.c (STDERR_FILENO): Likewise. * tests/test-posix_spawn1.c (STDIN_FILENO, STDOUT_FILENO) (STDERR_FILENO): Likewise. * tests/test-posix_spawn2.c (STDIN_FILENO, STDOUT_FILENO) (STDERR_FILENO): Likewise. * tests/test-posix_spawn3.c (STDIN_FILENO, STDOUT_FILENO) (STDERR_FILENO): Likewise. Reported by Elbert Pol. Signed-off-by: Eric Blake <ebb9@byu.net>