analyzer: consider initializers for globals [PR96651]

analyzer: consider initializers for globals [PR96651]

PR analyzer/96651 reports a false positive in which a global
that can't have been touched yet is checked in "main".  The analyzer
fails to reject code paths in which the initial value of the global
makes the path condition impossible.

This patch detects cases where the code path begins at the entrypoint
of "main", and extracts values from initializers for globals that
can't have been touched yet, rather than using a symbolic
"INIT_VAL(REG)", fixing the false positive.

gcc/analyzer/ChangeLog:
	PR analyzer/96651
	* region-model.cc (region_model::called_from_main_p): New.
	(region_model::get_store_value): Move handling for globals into...
	(region_model::get_initial_value_for_global): ...this new
	function, and add logic for extracting values from decl
	initializers.
	* region-model.h (decl_region::get_svalue_for_constructor): New
	decl.
	(decl_region::get_svalue_for_initializer): New decl.
	(region_model::called_from_main_p): New decl.
	(region_model::get_initial_value_for_global): New.
	* region.cc (decl_region::maybe_get_constant_value): Move logic
	for getting an svalue from a CONSTRUCTOR node to...
	(decl_region::get_svalue_for_constructor): ...this new function.
	(decl_region::get_svalue_for_initializer): New.
	* store.cc (get_svalue_for_ctor_val): Rewrite in terms of
	region_model::get_rvalue.
	* store.h (binding_cluster::get_map): New accessor.

gcc/testsuite/ChangeLog:
	PR analyzer/96651
	* gcc.dg/analyzer/pr96651-1.c: New test.
	* gcc.dg/analyzer/pr96651-2.c: New test.