For another universal library I need to combine 2 existing dylibs (here x86 and x64) into a single universal lib. How can I do that without re-building the existing libraries?
Actually, it's extremely easy to do once you know it. There's a tool called lipo that can do a number of things with dylibs. One is to combine two (or more) libraries. For example:
lipo lib1.dylib lib2.dylib -output combined.dylib -create
where lib1 could be an i386 and lib2 an x86_64 arch type. It will create a dylib in the local folder containing both archs.
来源：https://stackoverflow.com/questions/22783453/how-to-create-a-universal-dylib-from-pre-built-dylibs-for-each-architecture