Using miniz.c in multiple projects can cause symbol clashes about miniz HOT 5 OPEN

SDL2_image is one such library. When statically-compiled (eg when using 
MXE/MinGW), it usually results in link errors.

Ok - That's a good idea, and I'll get this or something like it into the next 
release (v1.16).

I ported to c/h file to avoid duplicate symbol linking errors. Not sure it is 
the best approach, but it worked in my case and you can find notes about the 
issues I ran into at 
https://github.com/mapnik/mapnik/blob/master/include/mapnik/miniz_png.hpp#L34-L4
1

+1 for separate .c/.h files. When building a library, this would allow miniz to 
inherit any library-wide build settings for symbol visibility, rather than 
defining its own. It would also work in some odd situations where including a 
.c file doesn't work (e.g. when building with qmake — 
https://bugreports.qt-project.org/browse/QTBUG-24906). Right now I'm working 
around this with `MINIZ_HEADER_FILE_ONLY`. 

When you implement building a shared library, please don't forget to version 
the library properly. (E.g. the feature is called SONAME in ELF executable 
format.) Proper versioning ensures that if the library changes ABI, 
applications built against older incompatible library version get notified at 
start.