Work around fussy zlib on macOS

Author: kornelski

CMakeLists.txt

@@ -681,9 +681,14 @@ if(ENABLE_STATIC)
   endif()
 
   if(PNG_SUPPORTED)
+    if (APPLE)
+      find_package(ZLIB REQUIRED) # macos doesn't have static zlib
+    endif()
     set(CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_STATIC_LIBRARY_SUFFIX})
     find_package(PNG 1.6 REQUIRED)
-    find_package(ZLIB REQUIRED)
+    if (NOT APPLE)
+      find_package(ZLIB REQUIRED)
+    endif()
     target_include_directories(cjpeg-static PUBLIC ${PNG_INCLUDE_DIR} ${ZLIB_INCLUDE_DIR})
     target_link_libraries(cjpeg-static ${PNG_LIBRARY} ${ZLIB_LIBRARY})
   endif()