glsl: Allow invariant qualifer in block members in desktop OpenGL.

glsl: Allow invariant qualifer in block members in desktop OpenGL.

Feedback from Khronos is that 'invariant' should be allowed on block
members for desktop OpenGL. Fix piglit regression added by fe1e89a0:
invariant-qualifier-in-out-block-01.vert

v2:
- Allow it for in/out blocks in OpenGL ES too, so when OES_shader_io_blocks
is supported we don't need to do any change (Timothy)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89330
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>