glslang -> SPV: improved support for do-while/continue.  Contributed by David Neto (dneto@google.com).

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@31205 e7fa87d3-cd2b-0410-9028-fcbf551c1848