pthread-functions.h includes. Include setxid.h. Use
INLINE_SETXID_SYSCALL macro instead of INLINE_SYSCALL, kill the
HAVE_PTR__NPTL_SETXID guarded snippets.
* sysdeps/unix/sysv/linux/alpha/setresgid.c: New file.
* sysdeps/unix/sysv/linux/alpha/setresuid.c: New file.
* sysdeps/unix/sysv/linux/alpha/setreuid.c: New file.