This implements a recent change to the GLSL specification to enforce
this ill-defined situation.

Also, generally allow ES variable indexing of in/out blocks.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@27714 e7fa87d3-cd2b-0410-9028-fcbf551c1848