Issue an internal warning on first deprecated function call

[Andrew Cagney]

> A variation on the above idea is to scan a newly created gdbarch
>> struct to see if any deprecated functions are being used.  If so,
>> print only one message per session.  (I.e, instead of seeing N
>> messages from N deprecated function, you'd only see one message for
>> the whole lot.) The nuisance factor could be cut back even further if
>> we arrange for .gdbinit setting which can be used to disable such
>> messages.
> 
> 
> I like the 'once per session' idea.
> Can we make the that message a rather largish banner?

My intent is for it to use ``internal-warning'' which means it will look 
something like this:

(gdb) maint internal-error
/home/scratch/GDB/src/gdb/maint.c:121: gdb-internal-error: internal 
maintenance
An internal GDB error was detected.  This may make further
debugging unreliable.  Quit this debugging session? (y or n) n

Create a core file containing the current state of GDB? (y or n) n
(gdb)

s/error/warning/

Since the user is going to need to interact with this, they will get 
very annoyed with it pretty quick.  This is why I'm also proposing 
another command for gaging it :-)

I think ``internal-warning'' is correct since there is a very very good 
chance that the deprecated interface will have been [unintentionally] 
broken by the introduction of the new mechanisms.

Andrew