Turn on CFG_TOYBOX_DEBUG for valgrind.

Turn on CFG_TOYBOX_DEBUG for valgrind.

https://github.com/landley/toybox/commit/047bcb8e7d37847b96dbf621ea22ff00e9541d32
only made ls valgrind-clean if CFG_TOYBOX_DEBUG is defined. So let's define
that.

The only other stuff this turns on is various bits of error checking that it
doesn't seem unreasonable to run with. If this becomes a problem in future,
we can lobby to have CFG_TOYBOX_VALGRIND_CLEAN broken out of
CFG_TOYBOX_DEBUG.

Change-Id: I8f89459d50f0fc976b225f1bfa01f55ac85de4b5