* Makefile.in (ALL_SUBDIRS): New variable.

	(subdirs, clean, distclean): Use it.
	* gdb.arch/Makefile.in: Clean up Makefile.  Remove rules for
	regenerating Makefile, since it is generated from the top level.
	* gdb.asm/Makefile.in: Likewise.
	* gdb.base/Makefile.in: Likewise.
	* gdb.c++/Makefile.in: Likewise.
	* gdb.disasm/Makefile.in: Likewise.
	* gdb.java/Makefile.in: Likewise.
	* gdb.mi/Makefile.in: Likewise.
	* gdb.threads/Makefile.in: Likewise.
	* gdb.trace/Makefile.in: Likewise.