Update Makefiles to support Emscripten

- Use BIN.SUFFIX instead of BIN_EXTENSION for consistency
- Don't build static/shared lib if the filename isn't specified
- Examples should depend on static lib if shared isn't built
- Allow overriding release-mode defines for LOG/TLS
- Add SYSTEM=emscripten config
Add unsigned_length() for EMSCRIPTEN in boost/print/detail.hpp
Update scripts and generated sources for Emscripten

- Add REGAL_SYS_EMSCRIPTEN and REGAL_SYS_EMSCRIPTEN_STATIC defines
- Guard extension static EGL entry points on non-EMSCRIPTEN
Update core sources for Emscripten/WebGL
More EMSCRIPTEN/webgl fixes
Implement some GL_FOG getters
Add GL_ARB_multi_bind
Merge and harmonize src/apitrace with upstream
Merging Emscripten changes from Vladimir Vukicevic, except Makefile
More entry points for RegalDispatchGMock