gdb: make interps_notify work with references

gdb: make interps_notify work with references

A subsequent patch changes the interp::on_solib_loaded and
interp::on_solib_unloaded methods to take references.  This highlighted
that interps_notify did not work with reference parameters.

Fix that by changing interps_notify's `args` arg to be a universal
reference (&&).  Change the type of the method to be auto-deduced as an
additional template parameter, otherwise the signature of the callback
function would never match:

      CXX    interps.o
    /home/simark/src/binutils-gdb/gdb/interps.c: In function ‘void interps_notify_signal_received(gdb_signal)’:
    /home/simark/src/binutils-gdb/gdb/interps.c:378:18: error: no matching function for call to ‘interps_notify(void (interp::*)(gdb_signal), gdb_signal&)’
      378 |   interps_notify (&interp::on_signal_received, sig);
          |   ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    /home/simark/src/binutils-gdb/gdb/interps.c:363:1: note: candidate: ‘template<class ... Args> void interps_notify(void (interp::*)(Args ...), Args&& ...)’
      363 | interps_notify (void (interp::*method) (Args...), Args&&... args)
          | ^~~~~~~~~~~~~~
    /home/simark/src/binutils-gdb/gdb/interps.c:363:1: note:   template argument deduction/substitution failed:
    /home/simark/src/binutils-gdb/gdb/interps.c:378:18: note:   inconsistent parameter pack deduction with ‘gdb_signal’ and ‘gdb_signal&’
      378 |   interps_notify (&interp::on_signal_received, sig);
          |   ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Change-Id: I0cd9378e24ef039f30f8e14f054f8d7fb539c838
Approved-By: Pedro Alves <pedro@palves.net>
Reviewed-By: Reviewed-By: Lancelot Six <lancelot.six@amd.com>