That depends on what your "decent code base" is, what it is meant to accomplish, how much coverage of your library is going to exist in your mobile app, whether

That depends on what your "decent code base" is, what it is meant to accomplish, how much coverage of your library is going to exist in your mobile app, whether (and how often) you will actually re-use the core libraries, etc. Realistically, what the OP is doing is pushing the maintenance and platform-specific code into a different part of the stack. In either case, code in different languages, with different native-interface specifications and idioms, is required to be written and maintained. Unless you have some certainty that the maintenance of the multiple different platform wrapper code bases will be less laborious than simply writing platform-specific code, it's probably not worth it. In the worst case, for example, a new function in C or C++ that you write may have to have one (or more!) new functions written in the platform-specific wrapper code in order to utilize it.