Disable tower socket runtest

The projects-pim-run-pass-tower.exp test blocks indefinitely
on some platforms.  This patch disables it for now - it should
be enabled once a cross platform fix for RTint.mod is found.

gcc/testsuite/ChangeLog:

	* gm2/projects/pim/run/pass/tower/projects-pim-run-pass-tower.exp
	(gm2_run_tower_test): New global variable.  Add conditional
	before invoking gm2-local-exec.

Signed-off-by: Gaius Mulley <gaiusmod2@gmail.com>