Multi-arch and user-control of architecture flags

[Richard Earnshaw <rearnsha@arm.com>]

More random thoughts that I thought worth writing down before I forget 
them...

The current way to allow for a user to control some aspect of a target is 
to add a "set" command so that they can control a flag, for example, the 
ARM target has

  set apcs32 true/flase

to control whether the debugger should work with the processor in 26-bit 
mode or 32-bit mode.

As we move towards supporting multiple processors in a single GDB this is 
going to become increasingly confusing if we continue down this line, and 
it will become very unclear (to the poor user) which options apply to 
which target.

So how feasible would it be to extend the "set" and "show" commands so 
that they could sub-set the information?  For example, to allow

  set <target> <var> <value>

and 

  show <target> <var>

or even

  show <target>

to show all variables specific to the target.

If this isn't particularly practical, then perhaps we need a new command 
(tset/tshow?) that provides this.

R.