libjxl is a library for encoding and decoding JPEG XL images, from
[https://github.com/libjxl/libjxl].

How to update the extra headers:
================================

The extra header files (jxl_cms_export.h, jxl_export.h, jxl_threads_export.h,
version.h) can be generated with:

(cd workdir/UnpackedTarball/libjxl/ && cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_TESTING=OFF)

If new header files are generated in this way, they will be placed in
workdir/UnpackedTarball/libjxl/lib/include/jxl/.

There are more detailed build instructions in
workdir/UnpackedTarball/libjxl/BUILDING.md (for Linux) and
workdir/UnpackedTarball/libjxl/developing_in_windows_vcpkg.md (for Windows). (A
full build isn't necessary to generate the headers, only the first cmake
command without --build.)
