glsl: handle interactions between EXT_gpu_shader4 and texture extensions

also, EXT_texture_buffer_object has to be enabled separately.

Reviewed-by: Eric Anholt <eric@anholt.net>
14 jobs for !667 with ext_gpu_shader4 in 11 minutes and 55 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Containers Build
passed #261280
debian

00:00:21

 
  Build+Test
passed #261282
meson-clang

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passed #261288
meson-gallium-clover-llvm

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passed #261289
meson-gallium-clover-llvm39

00:02:36

passed #261287
meson-gallium-drivers-other

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passed #261286
meson-gallium-radeonsi

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passed #261290
meson-gallium-st-other

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passed #261281
meson-gallium-swr

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meson-glvnd

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passed #261284
meson-loader-classic-dri

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passed #261283
meson-vulkan

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passed #261292
scons-llvm

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passed #261291
scons-nollvm

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passed #261293
scons-swr

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