analyzer: fix false +ves from -Wanalyzer-tainted-array-index with unsigned char index...

analyzer: fix false +ves from -Wanalyzer-tainted-array-index with unsigned char index [PR106229]

gcc/analyzer/ChangeLog:
	PR analyzer/106229
	* analyzer.h (compare_constants): New decl.
	* constraint-manager.cc (compare_constants): Make non-static.
	* sm-taint.cc: Add include "fold-const.h".
	(class concrete_range): New.
	(get_possible_range): New.
	(index_can_be_out_of_bounds_p): New.
	(region_model::check_region_for_taint): Reject
	-Wanalyzer-tainted-array-index if the type of the value makes it
	impossible for it to be out-of-bounds of the array.

gcc/testsuite/ChangeLog:
	PR analyzer/106229
	* c-c++-common/analyzer/taint-index-pr106229.c: New test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>