analyzer: add CWE identifier URLs to docs

gcc/analyzer/ChangeLog:
	* sm-malloc.cc (free_of_non_heap::emit): Add comment about CWE.
	* sm-taint.cc (tainted_size::emit): Likewise.

gcc/ChangeLog:
	* doc/invoke.texi (-fdiagnostics-show-cwe): Use uref rather than
	url.
	(Static Analyzer Options): Likewise.  Add urefs for all of the
	warnings that have associated CWE identifiers.

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