More selective disabling of 693- only fails at O3

git-svn-id: https://svn.mcs.anl.gov/repos/exm/sfw/stc/trunk@13619 dc4e9af1-7f46-4ead-bba6-71afc04862de
Fix issue 717 (partially) - don't run value numbering on dead code blocks.

git-svn-id: https://svn.mcs.anl.gov/repos/exm/sfw/stc/trunk@13620 dc4e9af1-7f46-4ead-bba6-71afc04862de