In the xservers configure.ac is a section where it is checked if the libdrm version is new enough:
if test "x$DRM" = xyes; then
dnl 2.4.46 is required for cursor hotspot support.
PKG_CHECK_EXISTS(libdrm >= 2.4.46)
But the modesetting driver is enabled anyway.
I experienced this problem with xorg-xserver 1.17.2 in a yocto build environment.
May be something like
PKG_CHECK_EXISTS([libdrm >= 2.4.46], [XORG_DRIVER_MODESETTING=yes], [XORG_DRIVER_MODESETTING=no])
would solve the problem.
Author: Adam Jackson <firstname.lastname@example.org>
Date: Wed Jan 27 11:50:13 2016 -0500
modesetting: Require sufficiently new libdrm
Signed-off-by: Adam Jackson <email@example.com>
Reviewed-by: Alex Deucher <firstname.lastname@example.org>
Reviewed-by: Julien Cristau <email@example.com>