xwayland/glx: Enable sRGB fbconfigs

We turn this on if the GL underneath us can enable GL_FRAMEBUFFER_SRGB.
However we don't generate both capable and incapable configs, which is
unlike the DRI backend, but matches NVIDIA.
5 jobs for glx-egl-srgb-fbconfigs in 5 minutes and 31 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Docker Image
passed #9347778
debian-buster

00:00:37

 
  Build And Test
passed #9347779
autotools

00:04:54

passed #9347780
meson

00:02:42

passed #9347781
meson-noglamor

00:02:04

passed #9347782
mingw-cross-build

00:01:24