glsl_compiler: Enable any extension that any Mesa driver enables
glsl_compiler: Enable any extension that any Mesa driver enables

The only GLSL extension that is not enabled is AMD_vertex_shader_layer.
I think the standalone-compiler could enable this (as shading language
support is complete), but no driver enables it.

Signed-off-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>
Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

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