[RFA 00/13] Makefile simplifications and subdirification

[Tom Tromey <tom at tromey dot com>]

This is a follow-on to Yao's earlier patch to move some object files
to subdirectories.

This first changes the approach to making such subdirectories, to make
it simpler on subsequent patches.  Then it moves object files to
subdirs, removing hand-maintained lists of .o files in favor of
patsubst, following the "don't repeat yourself" principle.

The last patches apply similar cleanups more generically.  The net
result is the removal of many redundant lines of code.

I did not touch common/ in this series.  I started this, but due to
commmon/common.host, a change here would require touching gdbserver as
well, which I did not want to do.

I think there are more cleanups available to be done; I just did not
do them.  A good end goal, I think, would be to make it so that only
source files are explicitly named in the Makefile, with the
intermediate names being generated from the source lists.  This would
make adding new source files much simpler.

Tested by rebuilding.  I also did a build with
--disable-{python,guile,tui,gdbmi} (did you know you can disable MI?).
You may need to do a clean build if this lands; though I am not
completely certain.

Tom