[Piglit] [PATCH 0/6] Clean up GLSL linker tests

[Ian Romanick]

The first two patches replace a pile of C code tests with a simple
test framework for linker tests.  A list of shaders and a pass / fail
result is passed to glsl-link-test.  The test passes if linking
produces the expected result.

Patch 3/6 makes an exist test expect the behavior mandated by the GLSL
4.20 spec.  The previous behavior was, basically, unimplementable.

Patches 4/6 and 5/6 add a couple new variations.

Patch 6/6 simplifies one of the existing tests.