GL_ARB_enhanced_layouts, final.  #extension tests, built-in constants, and bug fix for non-constant expression in layout(...=expr).


git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@25220 e7fa87d3-cd2b-0410-9028-fcbf551c1848