analyzer: fix 'errno' on Solaris and OS X [PR107807]

gcc/analyzer/ChangeLog:
	PR analyzer/107807
	* region-model-impl-calls.cc (register_known_functions): Register
	"___errno" and "__error" as synonyms  for "__errno_location".

gcc/testsuite/ChangeLog:
	PR analyzer/107807
	* gcc.dg/analyzer/errno-___errno.c: New test.
	* gcc.dg/analyzer/errno-__error.c: New test.
	* gcc.dg/analyzer/errno-global-var.c: New test.

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