Test inter- and intra-stage gl_PerVertex matching rules.

These tests verify the following linkage rules, from GLSL 4.10:

1. If multiple shaders using members of a built-in block belonging to
the same interface are linked together in the same program, they must
all redeclare the built-in block in the same way, as described in
section 4.3.7 "Interface Blocks" for interface block matching, or a
link error will result.

2. It will also be a link error if some shaders in a program redeclare
a specific built-in interface block while another shader in that
program does not redeclare that interface block yet still uses a
member of that interface block.