Xorg libthr coredump

Trying to configure and start Xorg on my Lenovo ThinkPad T460p. my pciconf -lv | grep -A 4 vga output.

vgapci1@pci0:0:2:0:   class=0x030000 card=0x505017aa chip=0x191b8086 rev=0x06 hdr=0x00
    vendor     = 'Intel Corporation'
    device     = 'HD Graphics 530'
    class      = display
    subclass   = VGA
vgapci0@pci0:2:0:0:   class=0x030200 card=0x505017aa chip=0x134d10de rev=0xa2 hdr=0x00
    vendor     = 'NVIDIA Corporation'
    device     = 'GM108M [GeForce 940MX]'
    class      = display
    subclass   = 3D

when I do Xorg -configure I get.
X.Org X Server 1.18.4
Release Date: 2016-07-19
X Protocol Version 11, Revision 0
Build Operating System: FreeBSD 11.0-SYNTH amd64
Current Operating System: FreeBSD zvartnots 11.0-RELEASE-p1 FreeBSD 11.0-RELEASE-p1 #0 r306420: Thu Sep 29 01:43:23 UTC 2016     root@releng2.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC amd64
Build Date: 04 July 2017  01:54:44AM
Current version of pixman: 0.34.0
   Before reporting problems, check http://wiki.x.org
   to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
   (++) from command line, (!!) notice, (II) informational,
   (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Tue Jul  4 16:47:45 2017
List of video drivers:
(++) Using config file: "/root/xorg.conf.new"
(EE) Backtrace:
(EE) 0: /usr/local/bin/Xorg (OsInit+0x38a) [0x5abfba]
(EE) 1: /lib/libthr.so.3 (_pthread_sigmask+0x50d) [0x8025cebbd]
(EE) 2: /lib/libthr.so.3 (_pthread_getspecific+0xe9f) [0x8025ceacf]
(EE) 3: ? (?+0xe9f) [0x800000000032]
(EE) 4: ? (?+0xe9f) [0xe9f]
(EE) 5: /usr/local/bin/Xorg (InitOutput+0x11ea) [0x47faca]
(EE) 6: /usr/local/bin/Xorg (remove_fs_handlers+0x38b) [0x43b48b]
(EE) 7: /usr/local/bin/Xorg (_start+0x17f) [0x42506f]
(EE) 8: ? (?+0x17f) [0x80083217f]
(EE) Segmentation fault at address 0x0
Fatal server error:
(EE) Caught signal 11 (Segmentation fault). Server aborting
Please consult the The X.Org Foundation support
    at http://wiki.x.org
 for help.
(EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
(EE) Server terminated with error (1). Closing log file.

usually people say delete the old version of LLVM, however pkg info | grep llvm says

any idea what to do? :)
SirDice thank you for the link. I've stopped doing that! :)

now, I've installed x11/nvidia-driver and run nvidia-xconfig and added my BusID, after doing startx I get a black screen, I assume this is a problem since I have NVidia with Optimus technology. any way around that?
As far as I know Optimus is still problematic. Can you disable one of the cards in the BIOS/UEFI?