- the built-in constants
 - built-in variable declarations, some dependent on gl_MaxPatchVertices
 - layout qualifier for vertices (shared with geometry shader max_vertices)
 - layout qualifiers for vertex spacing, vertex order, point mode, and primitive type
 - link semantics for layout qualifiers

Still TBD:
 - patch qualifier and arrayed input handling
 - sizing of gl_out[]
 - additional semantic checking
 - supporting the extension on version 150

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@24468 e7fa87d3-cd2b-0410-9028-fcbf551c1848