add TINYXML2_EXPORT define when building shared lib

otherwise it exports no symbols and msvc does not create import .lib

CMakeLists.txt

@@ -53,6 +53,7 @@ if(BUILD_STATIC_LIBS)
 endif(BUILD_STATIC_LIBS)
 add_library(tinyxml2 SHARED tinyxml2.cpp tinyxml2.h)
 set_target_properties(tinyxml2 PROPERTIES
+        COMPILE_DEFINITIONS "TINYXML2_EXPORT"
 	VERSION "${GENERIC_LIB_VERSION}"
 	SOVERSION "${GENERIC_LIB_SOVERSION}")