x11-drivers/xf86-video-vesa: Check for CONFIG_DEVMEM.

Bug: https://bugs.gentoo.org/577360

x11-drivers/xf86-video-vesa/xf86-video-vesa-2.3.4.ebuild

@@ -1,9 +1,9 @@
-# Copyright 1999-2016 Gentoo Foundation
+# Copyright 1999-2017 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 # $Id$
 
 EAPI=5
-inherit xorg-2
+inherit linux-info xorg-2
 
 DESCRIPTION="Generic VESA video driver"
 KEYWORDS="-* alpha amd64 ia64 x86 ~amd64-fbsd ~x86-fbsd"
@@ -12,3 +12,16 @@ IUSE=""
 RDEPEND=">=x11-base/xorg-server-1.6
 	>=x11-libs/libpciaccess-0.12.901"
 DEPEND="${RDEPEND}"
+
+pkg_pretend() {
+	linux-info_pkg_setup
+
+	if ! linux_config_exists || ! linux_chkconfig_present DEVMEM; then
+		echo
+		ewarn "This driver requires /dev/mem support in your kernel"
+		ewarn "  Device Drivers --->"
+		ewarn "    Character devices  --->"
+		ewarn "      [*] /dev/mem virtual device support"
+		echo
+	fi
+}