root-uid: new module

root-uid: new module

This is for portability to Tandem's NonStop Kernel.
* lib/root-uid.h, modules/root-uid: New files.
* lib/euidaccess.c, lib/pt_chown.c, lib/unlinkdir.c:
* lib/write-any-file.c, tests/test-sethostname2.c:
Include "root-uid.h".
* lib/euidaccess.c (euidaccess):
* lib/pt_chown.c (main):
* lib/unlinkdir.c (cannot_unlink_dir):
* lib/write-any-file.c (can_write_any_file):
* m4/mknod.m4 (gl_FUNC_MKNOD):
* tests/test-sethostname2.c (geteuid, main):
Don't assume ROOT_UID == 0.
* modules/euidaccess (Depends-on):
* modules/pt_chown (Depends-on):
* modules/sethostname-tests (Depends-on):
* modules/unlinkdir (Depends-on):
* modules/write-any-file (Depends-on):
Add root-uid.