Trying to run gzdoom on an intel igpu with OpenGL 2.1 results in a segfault without any messages:
$ gzdoom
GZDoom 2.5pre-340-gd407aa3 - 2017-04-13 22:16:26 +0200 - SDL version
Compiled on Apr 14 2017
M_LoadDefaults: Load system defaults.
W_Init: Init WADfiles.
adding /usr/share/games/doom-data/gzdoom.pk3, 711 lumps
adding /home/lucas/.config/gzdoom/doom2.wad, 2919 lumps
I_Init: Setting up machine state.
CPU Vendor ID: GenuineIntel
Name: Intel(R) Core(TM)2 CPU T7600 @ 2.33GHz
Family 6, Model 15, Stepping 6
Features: MMX SSE SSE2 SSE3 SSSE3
I_InitSound: Initializing OpenAL
Opened device No Output
EFX enabled
V_Init: allocate screen.
S_Init: Setting up sound.
ST_Init: Init startup screen.
Checking cmd-line parameters...
S_InitData: Load sound definitions.
G_ParseMapInfo: Load map definitions.
Texman.Init: Init texture manager.
ParseTeamInfo: Load team definitions.
LoadActors: Load actor definitions.
script parsing took 220.50 ms
R_Init: Init Doom refresh subsystem.
DecalLibrary: Load decals.
M_Init: Init menus.
P_Init: Init Playloop state.
ParseSBarInfo: Loading custom status bar definition.
D_CheckNetGame: Checking network game status.
player 1 of 1 (1 nodes)
Using video driver x11
*** Fatal Error ***
!!! Failed to exec debug process
Segmentation fault
The gdb stack indicates a segfault at function CollectExtensions() from gl_interface.cpp:
CollectExtensions () at /var/tmp/portage/games-fps/gzdoom-9999/work/gzdoom-9999/src/gl/system/gl_interface.cpp:55
55 in /var/tmp/portage/games-fps/gzdoom-9999/work/gzdoom-9999/src/gl/system/gl_interface.cpp
(gdb) s
[New Thread 0x7fffe73a5700 (LWP 22734)]
[Thread 0x7fffe6ba4700 (LWP 22733) exited]
56 in /var/tmp/portage/games-fps/gzdoom-9999/work/gzdoom-9999/src/gl/system/gl_interface.cpp
(gdb) s
[Thread 0x7fffe73a5700 (LWP 22734) exited]
[New Thread 0x7fffe73a5700 (LWP 22853)]
Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()
Probably because GL_NUM_EXTENSIONS is not defined on OpenGL < 3.0. | 
