The ABI compatibility feature was developed by the current maintainer of
libjpeg-turbo with an eye toward eventual inclusion in libjpeg-turbo (once
other features are added to libjpeg-turbo that necessitate the inclusion.)
Thus, it is easy to ensure that the DLL function ordinals will be synchronized
between libjpeg-turbo and mozjpeg.  However, it still makes sense to allow for
a little bit of breathing room, just in case.  Thus, this patch uses ordinals
starting at 200 for the accessor functions.  It would probably make sense to
start the decompressor functions at ordinal 300, once they are implemented.