update waf to 2.0.18 with c_emscripten compiler check support (issue #806)
update waf to 2.0.18 with c_emscripten compiler check support (issue #806)

This waf binary contains the support for detecting the emscripten clang compiler during the `./waf configure` process.

  `python waf-light --tools=c_emscripten`

using the waf 2.0.18 source.
See https://waf.io/book/#_download_and_installation for a description
of this process

MTG/essentia,MTG/essentia,MTG/essentia,MTG/essentia,MTG/essentia