glslang front-end: track column numbers (they don't go anywhere yet, just get tracked).  Andrew Woloszyn <awoloszyn@google.com>.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@31506 e7fa87d3-cd2b-0410-9028-fcbf551c1848