sm-signal.cc was failing to warn about the use of an fprintf call in a
signal handler when the signal handler function was non-static.

The root cause was a failure to copy global sm-state within
sm_state_map::clone_with_remapping as called by
program_state::can_merge_with_p, which led to the exploded node for
the entrypoint to the handler in the "normal" state being erroneously
reused for the "in_signal_handler" state, thus losing the global state,
and thus failing to warn.

This patch fixes the above, so that non-equal global sm-state values
prevent merger of program_state, thus requiring separate exploded nodes
for the "normal" and "in signal handler" states, and thus triggering
the warning for the reproducer.

gcc/analyzer/ChangeLog:
	* program-state.cc (sm_state_map::clone_with_remapping): Copy
	m_global_state.
	(selftest::test_program_state_merging_2): New selftest.
	(selftest::analyzer_program_state_cc_tests): Call it.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/signal-6.c: New test.