Tessellation partial implementation (not ready for use yet), including:

- 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

Test/baseResults/420.geom.out

@@ -126,4 +126,8 @@ ERROR: Linking geometry stage: Missing entry point: Each stage requires one "voi
 ERROR: Linking geometry stage: At least one geometry shader must specify an output layout primitive
 ERROR: Linking geometry stage: At least one geometry shader must specify a layout(max_vertices = value)
 
+invocations = 0
+max_vertices = 0
+input primitive = triangles
+output primitive = none