!UPSTREAM: glsl: Error check redeclarations of gl_PerVertex.

This patch verifies that the gl_PerVertex input interface block may
only be redeclared as gl_in[], and that the gl_PerVertex output
interface block may only be redeclared without an interface name.

TODO:
- Move prior to "glsl: Support redeclaration of VS and GS gl_PerVertex output."
- Make sure gl_PerVertex can't be redeclared as a uniform.