Generate one build target for all shader headers
Generate one build target for all shader headers

Simplifies projects generated from CMake

cleeus/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es