[RFC] Testsuite: permit simple transformation of gdb_expect code

[Joel Brobecker]

>   I would like to insert a no-op change to lib/gdb.exp that allows
>   easily to write a transformation function (that can be inside the
>   target board file).  The idea is to simply add a global variable
>   named `transform_gdb_expect_code' that defaults to empty.

No objection from my end in principle; I guess there is no way to
make that decision automatic? In AdaCore's testsuite, we get
the version information in GDB and determine from there the host
and target, and that allows to whether or not certain features
are available, etc.

In terms of implementation, rather than having an empty global,
perhaps it'd be just as simple to test its existence?  Just thinking
out loud...

-- 
Joel