QXcbIntegration: cannot create platform OpenGL context

[sbna]

Hi all,

I successfully compiled Qt5.9.1 on a HPC compute node without graphics card using the MESA opengl implementation (v17.2.3) and llvmpipe as software rasterizer.
I connect to the node using TurboVNC. Glxgears and Qt4-opengl applications works fine, but when I try to run a Qt5-opengl application I got the following error:
QXcbIntegration: Cannot create platform OpenGL context, neither GLX nor EGL are enabled

I know that EGL is not enabled but GLX should be since I compiled the MESA libraries with --enable-glx. Moreover, the qt configure reports in the config.summary that xcb-glx is found:

EGL .................................... no
OpenVG ................................. no
OpenGL:
Desktop OpenGL ....................... yes
OpenGL ES 2.0 ........................ no
OpenGL ES 3.0 ........................ no
OpenGL ES 3.1 ........................ no
QPA backends:
DirectFB ............................... no
EGLFS .................................. no
LinuxFB ................................ yes
VNC .................................... yes
Mir client ............................. no
X11:
Using system-provided XCB libraries .. no
EGL on X11 ........................... no
Xinput2 .............................. no
XCB XKB .............................. yes
XLib ................................. yes
XCB render ........................... yes
XCB GLX .............................. yes
XCB Xlib ............................. yes
Using system-provided xkbcommon ...... no

It's hard for me to understand the source of problems. Any hint about how to solve the issue or to better debug the problem is appreciated!

Simone.