qmlgl: Fix opengl header guard changes again

Reapply 3d708a5b in the correct place
after the iOS additions.
8 jobs from qmlgl-header in 15 minutes and 11 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #98947
gst indent

00:00:14

passed #98946
manifest

00:00:18

 
  Build
passed #98948
build fedora x86_64

00:02:26

 
  Test
passed #98949
check fedora

00:03:17

 
  Full Builds
passed #98950
build android arm64 api28

00:04:08

passed #98952
build cerbero cross win32

00:09:08

passed #98953
build cerbero cross win64

00:07:37

passed #98951
build cerbero fedora x86_64

00:07:42