add libdeflate support to libTIFF build

[Jeff McKenna]

• this is potentially a major speed improvement (35-50%)
• will require:
  • compiled libdeflate (in itself a challenge, from my initial research) : ​https://github.com/ebiggers/libdeflate
  • a recent libTIFF with this change: ​https://gitlab.com/libtiff/libtiff/-/merge_requests/158
  • future GDAL 3.2.0 with this change, so GDAL can take advantage of libdeflate: ​https://github.com/OSGeo/gdal/pull/3068

Some interesting speed comparisons with Zstandard compression (which was added to the MS4W 4.0.4 release) and libdeflate in this comment: ​https://github.com/OSGeo/gdal/pull/3068#issuecomment-710037119

So, MS4W users can choose from either compression/decompression method, on the user-side, when this is all added into MS4W.

Of course, the same blocker of PROJ 7 relates to this.

/me wonders if all this major effort of GDAL3+PROJ7+libdeflate+MapServer+FastCGI+PROJ-network-setup should absolutely be funded. I am facing a month's effort on this probably, and likely will be the first MapServer distribution to distribute/tackle all this, for users (as usual).

Setting the priority of this ticket to 'critical'.