glGetString on EGL always returns NULL on GLES2
Moving here from a bug observed in Firefox (https://bugzilla.mozilla.org/show_bug.cgi?id=1689207#c10).
If the GLES version is 2.0,
glGetString used in EGL will return
NULL while it appears to work normal on GLX (tested only on Intel). It does not matter which GL version is supported.
This can be easily tested by setting
MESA_GLES_VERSION_OVERRIDE=2.0 and running Firefox nightly with either
MOZ_X11_EGL=1 - haven't found another reproducer yet as
eglinfo doesn't use it (while glxinfo does).
This apparently affects a lot of older hardware.