support/testing: test_glxinfo load X11 modules in the right order

From [1]
"Xorg does not implement real dynamic linking and requires that its
modules get loaded in the right order."

From /var/log/Xorg.0.0.log:
 (II) LoadModule: "modesetting"
 (II) Loading /usr/lib/xorg/modules/drivers/modesetting_drv.so
 (EE) Failed to load /usr/lib/xorg/modules/drivers/modesetting_drv.so: /usr/lib/xorg/modules/drivers/modesetting_drv.so: undefined symbol: shadowRemove

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/1255661899

[1] https://forums.gentoo.org/viewtopic-p-8245578.html#8245578

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

support/testing/tests/package/test_glxinfo.py

@@ -32,7 +32,9 @@ class TestGlxinfo(infra.basetest.BRTest):
         BR2_TARGET_GENERIC_GETTY_PORT="ttyS0"
         BR2_TARGET_ROOTFS_EXT2=y
         # BR2_TARGET_ROOTFS_TAR is not set
-        """
+        BR2_ROOTFS_OVERLAY="{}"
+        """.format(
+          infra.filepath("tests/package/test_glxinfo/rootfs-overlay"))
 
     def wait_for_xserver(self):
         # xserver takes some time to start up

support/testing/tests/package/test_glxinfo/rootfs-overlay/etc/X11/xorg.conf.d/01-modules.conf

@@ -0,0 +1,11 @@
+
+# Xorg does not implement real dynamic linking and requires that its
+# modules get loaded in the right order.
+# https://forums.gentoo.org/viewtopic-p-8245578.html#8245578
+Section "Module"
+   Load "vgahw"
+   Load "fb"
+   Load "shadowfb"
+   Load "shadow"
+   Load "glamoregl"
+EndSection