analyzer: fix signal-handler registration location [PR95188]

analyzer: fix signal-handler registration location [PR95188]

PR analyzer/95188 reports that diagnostics from
-Wanalyzer-unsafe-call-within-signal-handler use the wrong
source location when reporting the signal-handler registration
event in the diagnostic_path.  The diagnostics erroneously use the
location of the first stmt in the basic block containing the call
to "signal", rather than that of the call itself.

Fixed thusly.

gcc/analyzer/ChangeLog:
	PR analyzer/95188
	* engine.cc (stmt_requires_new_enode_p): Split enodes before
	"signal" calls.

gcc/testsuite/ChangeLog:
	PR analyzer/95188
	* gcc.dg/analyzer/signal-registration-loc.c: New test.