[rfa/toplevel] Conditionalize GDB_TK

[Andrew Cagney]

>> The attached only adds the tk directories to the gdb dependency list
>> when the corresponding tk files are present.  That way `all-gdb'
>> doesn't build tk files (except when needed).
>> 
>> ok?
> 
> 
> Ok.


Thanks.

>> PS: Disclaimer, I cut/paste the configure changes.  Perhaps someone
>> able to regenerate configure should commit this?
> 
> 
> You don't have autoconf 2.13?

Which 2.13? :-)  Anyway I found the correct version, re-generated the 
file and committed (both GCC and SRC).

Andrew