Comment 4 for bug 1385947

In thinking about this a little, it seems that if optimization flags can be set in parser.conf to change the defaults, then use of '-O' shouldn't force skipping reading of the cache. Perhaps it would make sense to apply this patch but also to adjust the man page to state something long the lines of "if specifying '-O' on the command line, it probably makes sense to also specify '--skip-read-cache'".