Add VCMI_DLL flag for libvcmi

lib/CMakeLists.txt

@@ -132,6 +132,7 @@ set(lib_HEADERS
 
 add_library(vcmi SHARED ${lib_SRCS} ${lib_HEADERS})
 set_target_properties(vcmi PROPERTIES XCODE_ATTRIBUTE_LD_DYLIB_INSTALL_NAME "@rpath/libvcmi.dylib")
+set_target_properties(vcmi PROPERTIES COMPILE_DEFINITIONS "VCMI_DLL=1")
 target_link_libraries(vcmi minizip ${Boost_LIBRARIES} ${SDL_LIBRARY} ${ZLIB_LIBRARIES} ${RT_LIB} ${DL_LIB})
 
 set_target_properties(vcmi PROPERTIES ${PCH_PROPERTIES})