glsl: Cross-validate GS layout qualifiers while intrastage linking.

glsl: Cross-validate GS layout qualifiers while intrastage linking.

This gets piglit's geometry-basic test running.

TODO: Still need to validate that the GS layout qualifiers don't get used
in places they shouldn't (like an interface block, or a particular shader
input or output)

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>