Unify the 8 grammar productions for declaring variables. This greatly simplifies making changes for this set of productions.
This change also naturally picks up redeclarations of built-in arrays and the addition of the remaining linker objects of const, arrays, etc.
git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@23246 e7fa87d3-cd2b-0410-9028-fcbf551c1848
