QtQuick requests a shader language version which is not supported

I had originally reported this downstream at [1]. In attempting to debug why the task switcher (which uses qtquick) of the kwin window manager fails to render, I found out the following:

• When triggering the task-switcher, kwin reports
  QGLXContext: Failed to create dummy context

• Looking at the qt-sources, I found that QT_OPENGL_NO_SANITY_CHECK disables the sanity checking that triggers the dummy context creation.

• So trying with QT_OPENGL_NO_SANITY_CHECK=1 kwin_x11, triggering the task-switcher I get loads of
  QOpenGLShader::compile(Fragment): 0:1(10): error: GLSL 1.50 is not supported. Supported versions are: 1.10, 1.20, 1.30, 1.00 ES, 3.00 ES, 3.10 ES, and 3.20 ES

Somehow it looks like kwin is not using a core GL context with sufficiently high version? My graphics setup is

Vendor: Intel Open Source Technology Center (0x8086)
Device: Mesa DRI Intel(R) HD Graphics 530 (Skylake GT2) (0x191b)
Version: 17.2.0
Accelerated: yes
Video memory: 3072MB
Unified memory: yes
Preferred profile: core (0x1)
Max core profile version: 4.5
Max compat profile version: 3.0
Max GLES1 profile version: 1.1
Max GLES[23] profile version: 3.2

Downstream closed the issue pointing out that it is an upstream qtquick issue.

Apologies for not being able to provide much more infos, I'm neither familiar with the kwin codebase nor with qtquick.

[1] https://bugs.kde.org/show_bug.cgi?id=384045