analyzer: check for writes to consts via access attr [PR104793]

analyzer: check for writes to consts via access attr [PR104793]

This patch extends:
  -Wanalyzer-write-to-const
  -Wanalyzer-write-to-string-literal
so that they will check for __attribute__ ((access, ....) on calls to
externally-defined functions, and complain about read-only regions
pointed to by arguments marked with a "write_only" or "read_write"
attribute.

gcc/analyzer/ChangeLog:
	PR analyzer/104793
	* region-model.cc
	(region_model::check_external_function_for_access_attr): New.
	(region_model::handle_unrecognized_call): Call it.
	* region-model.h
	(region_model::check_external_function_for_access_attr): New decl.
	(region_model::handle_unrecognized_call): New decl.

gcc/testsuite/ChangeLog:
	PR analyzer/104793
	* gcc.dg/analyzer/write-to-const-2.c: New test.
	* gcc.dg/analyzer/write-to-function-1.c: New test.
	* gcc.dg/analyzer/write-to-string-literal-2.c: New test.
	* gcc.dg/analyzer/write-to-string-literal-3.c: New test.
	* gcc.dg/analyzer/write-to-string-literal-4.c: New test.

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