Here. I know it's half-assed and ignores everything in make.conf, but I really don't feel like patching makefiles today. Works for me at least.
EAPI=3
inherit games
DESCRIPTION="An online multiplayer, free software engine for Doom and Doom II"
HOMEPAGE="http://odamex.net/"
SRC_URI="mirror://sourceforge/project/${PN}/Odamex/${PV}/${PN}-src-${PV}.tar.bz2"
S="${WORKDIR}/${PN}-src-${PV}"
LICENSE="GPL-2"
SLOT="0"
KEYWORDS="~x86 ~amd64"
IUSE=""
# Unfortunately odamex's makefile doesn't let us build server/client/launcher
# separately, so you have to take all of them for now.
# Also it ignores your CFLAGS setting.
DEPEND="x11-libs/wxGTK:2.8[X]
media-libs/libsdl
media-libs/sdl-mixer"
RDEPEND="${DEPEND}"
src_compile() {
emake odamex odasrv odalaunch/odalaunch || die
}
src_install() {
emake INSTALLDIR="${D}/${GAMES_BINDIR}" \
RESDIR="${D}/${GAMES_DATADIR}" install || die
newicon "${S}/media/icon_odamex_128.png" "odamex.png"
newicon "${S}/media/icon_odalaunch_128.png" "odalaunch.png"
make_desktop_entry odamex "Odamex" odamex
make_desktop_entry odalaunch "Odamex Launcher" odalaunch
}