Fixes building on Windows. I also decided to move the preprocessed jxl/version.h to our include/jxl instead of relying on moz.build in preprocessing the file. Future me should note to not forget to update the version number at that new file
This fixes building with MSVC for Windows.
Used old-configure to add the build option for enabling JPEG-XL support. Highway version: 1.0.2 libjxl version: 0.7.0