glsl: Allow non-constant UBO array indexing with GLSL4/ARB_gpu_shader5.
glsl: Allow non-constant UBO array indexing with GLSL4/ARB_gpu_shader5.

Signed-off-by: Chris Forbes <5dcac483e7a6e31a5cbe89f38cc69dff8ee93dac@ijw.co.nz>
Reviewed-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

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