glsl-1.50: Test compilation of interface blocks containing unsized arrays.

Although it's not explicitly stated in the GLSL 1.50 spec, unsized
arrays are allowed in interface blocks.

section 1.2.3 (Changes from revision 5 of version 1.5) of the GLSL
1.50 spec says:

    * Completed full update to grammar section.  Tested spec examples
      against it:

      ...

      * add unsized arrays for block members

And section 7.1 (Vertex and Geometry Shader Special Variables)
includes an unsized array in the built-in gl_PerVertex interface
block:

    out gl_PerVertex {
        vec4 gl_Position;
        float gl_PointSize;
        float gl_ClipDistance[];
    };

Furthermore, GLSL 4.30 contains an example of an unsized array
occurring inside an interface block.  From section 4.3.9 (Interface
Blocks):

    uniform Transform {  // API uses "Transform[2]" to refer to instance 2
        mat4           ModelViewMatrix;
        mat4           ModelViewProjectionMatrix;
        vec4           a[];  // array will get implicitly sized
        float          Deformation;
    } transforms[4];

This patch adds compiler tests to verify that in and out blocks can
contain unsized arrays.

Verified using the NVIDIA proprietary driver for Linux.
Test accuracy of dFdx and dFdy functions.

Mesa/i965 currently (as of commit 1cc3b90) has an inaccurate
implementation of dFdy() which produces the same results for every
pixel in an aligned 2x2 block.  This piglit test exposes the
inaccuracy.
gs: Test core GS inputs on GLSL 1.50
gs: Test corner case for triangle strip ordering with primitive restart.

Verified using the NVIDIA proprietary driver for linux.