driver: Fix memory leak [PR93019]

driver:finalize used by JIT clears the mdswitches pointer; if it was
allocated before, that leaks the memory.

2023-12-09  Costas Argyris  <costas.argyris@gmail.com>
	    Jakub Jelinek  <jakub@redhat.com>

	PR driver/93019
	* gcc.cc (driver::finalize): Call XDELETEVEC on mdswitches before
	clearing it.

Signed-off-by: Costas Argyris <costas.argyris@gmail.com>