drd: Build fix for ENABLE_DRD_CONSISTENCY_CHECKS

From: Ivo Raisr <ivosh@ivosh.net>


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13863 a5019735-40e9-0310-863c-91ae7b9d1cf9
coregrind/m_scheduler + drd: Rework r13862

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13864 a5019735-40e9-0310-863c-91ae7b9d1cf9