chown.c: split into separate files

This will make further uid/gid fixes simpler.

* fchownat.c: New file.
* chown.c (sys_fchownat: Move to fchownat.c.
(sys_chown, sys_fchown): Move to uid.c.
* Makefile.am (strace_SOURCES): Remove chown.c, add fchownat.c.
4 files changed