gs: Test core GS inputs on GLSL 1.50

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
gs: Test corner case for triangle strip ordering with primitive restart.

Verified using the NVIDIA proprietary driver (version 313.18) for linux.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
!UPSTREAM: Interface block redeclaration tests

TODO:
- Add more tests

- Split into a patch for the GLSL 4.10 redeclaration rules and a patch
  for other GLSL 1.50 issues (e.g. disallowing a variable inside an
  unnamed interface block to match the name of a previously declared
  global)

- Validate using NVIDIA proprietary driver