dev-lisp/mzscheme unsets CFLAGS. This causes some rather nasty breakages on certain systems, see bug #59506 (Required CFLAGS being killed metabug) for details.
there is a patch in http://bugs.gentoo.org/show_bug.cgi?id=91970 for incorporating mzscheme and drscheme in one ebuild. The drscheme ebuild is up to date and doesn't unset CFLAGS.
As of drscheme-360-r2 there is now an X use flag which when disabled results in mzscheme without drscheme. Mzscheme is no longer needed and has been masked for removal.
*** Bug 91970 has been marked as a duplicate of this bug. ***
Removing us from cc/assigned then.
mzscheme is now gone, use drscheme with -X use flag instead