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.
diff --git a/fchownat.c b/fchownat.c
new file mode 100644
index 0000000..95de6e4
--- /dev/null
+++ b/fchownat.c
@@ -0,0 +1,15 @@
+#include "defs.h"
+
+int
+sys_fchownat(struct tcb *tcp)
+{
+	if (entering(tcp)) {
+		print_dirfd(tcp, tcp->u_arg[0]);
+		printpath(tcp, tcp->u_arg[1]);
+		printuid(", ", tcp->u_arg[2]);
+		printuid(", ", tcp->u_arg[3]);
+		tprints(", ");
+		printflags(at_flags, tcp->u_arg[4], "AT_???");
+	}
+	return 0;
+}