Fix zlib.h not found in src/pngimage.h

[TimmvonderMehden]

compiling exif2lib with EXV_HAVE_LIBZ fails at least on windows because the cmake does not set the include path for zlib

[neheb]

NACK. This was fixed upstream. Backport 81bc63d with git cherry-pick -x.

ping @kmilos

[kmilos]

Wasn't this backported already?

[kmilos]

Wasn't this backported already?

Ah, not the same change @neheb

Note that this shouldn't really be necessary as the ZLIB::ZLIB IMPORTED target should also propagate its INTERFACE_INCLUDE_DIRECTORIES to exiv2lib:

https://gitlab.kitware.com/cmake/cmake/-/blob/4dc16577c5ccfba615ed2dfb36d3296c17da06e7/Modules/FindZLIB.cmake#L215-L216

So, better try to figure out why that is not happening instead of merging this straight away?

Btw, we do exactly the same for other IMPORTED targets (see CURL::libcurl, Iconv::Iconv, inih::inireader, inih::libinih), does it fail the same way for those? I think we would've heard about it by now...?

[kmilos]

Also note that our CI covers Windows builds (both shared and static), and there seems to be no problems compiling pngimage.cpp:

https://github.com/Exiv2/exiv2/actions/runs/13787654889/job/38559402541#step:8:387
https://github.com/Exiv2/exiv2/actions/runs/13787654889/job/38559403624#step:8:389

(Nor on any other platform...)