Few notes:
- Lots of deprecated SIMD intrinsic warnings & errors in JPEG-XL -> Highway; had to suppress erorrs to make project build.
- Moved couple of common link flags to cpp.Dockerfile (note: can't move `EXPORT_ES6` otherwise `configure` will fail).
- MODULARIZE=1 is no longer necessary and implied by EXPORT_ES6.
- EXPORT_NAME=... is no longer necessary in EXPORT_ES6.
- Changed visdif to also use EXPORT_ES6 and ENVIRONMENT=node instead of generic JS.
