make clean doesn't run in gdbserver/common

[Joel Brobecker]

> gdb/gdbserver/
> 
> 	* Makefile.in (CLEANDIRS, REQUIRED_SUBDIRS): New variable.
> 	(subdir_do): New make target.  Copied from gdb/Makefile.
> 	(maintainer-clean, realclean, distclean, clean): Call corresponding
> 	make targets in common/Makefile.

What happens if you do a "make distclean" on a platform where both GDB
& GDBserver get built automatically in one "make"? It looks like we
will first do a distclean in gdb/ first, deleting gdb/common/Makefile,
and then do a distclean in gdbserver/, which will try to do a distclean
a second time in gdb/common, no? The second one will fail due to the
missing Makefile.

-- 
Joel