New issue by sebu06 on void-packages repository

https://github.com/void-linux/void-packages/issues/20565

Description:
### System

* xuname:  
  Void 5.5.13_1 x86_64 GenuineIntel uptodate rrrrmdFFFF
* package:  
  mesa-20.0.3_1

### Expected behavior
Up to Mesa 19.3.4_1 I was able to run CAESES (proprietary CAD system) without any problems. With the current Mesa-libs, CAESES fails to start.

### Actual behavior
The following error message appears:
`libGL error: MESA-LOADER: failed to open iris (search paths /usr/lib/xorg/modules/drivers)
libGL error: failed to load driver: iris
libGL error: MESA-LOADER: failed to open iris (search paths /usr/lib/xorg/modules/drivers)
libGL error: failed to load driver: iris
libGL error: MESA-LOADER: failed to open swrast (search paths /usr/lib/xorg/modules/drivers)
libGL error: failed to load driver: swrast
QGLTempContext: Unable to create GL context.
init glwindow: context not valid!
[xcb] Unknown sequence number while processing queue
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
CAESES: xcb_io.c:260: poll_for_event: Assertion `!xcb_xlib_threads_sequence_lost' failed.
`
By looking at the strace info, Mesa 19.3.4_1 loads:
`[pid 28187] openat(AT_FDCWD, "/usr/lib/xorg/modules/drivers/tls/i965_dri.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
[pid 28187] openat(AT_FDCWD, "/usr/lib/xorg/modules/drivers/i965_dri.so", O_RDONLY|O_CLOEXEC) = 19`
whereas Mesa 20.0.3_1 loads:
`[pid 26302] openat(AT_FDCWD, "/usr/lib/xorg/modules/drivers/tls/swrast_dri.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
[pid 26302] openat(AT_FDCWD, "/usr/lib/xorg/modules/drivers/swrast_dri.so", O_RDONLY|O_CLOEXEC) = 19

[pid 26302] openat(AT_FDCWD, "/usr/lib/xorg/modules/drivers/tls/iris_dri.so", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
[pid 26302] openat(AT_FDCWD, "/usr/lib/xorg/modules/drivers/iris_dri.so", O_RDONLY|O_CLOEXEC) = 20`

If necessary, I can provide full strace output for both mesa versions, but maybe this is enough to point into the right direction. I tried modesetting and xf86-video-intel - no difference.

Thanks for the help, 
Sebastian