Minimal, in the sense that this will only allow flatbuffers.h +
generated code to work. Everything else (tests, parsing, reflection
etc.) may still not compile with stlport.

Functionality has been reduced, some utility functions are not
available.

Tested: on Linux (no stlport), Android (stlport).

Change-Id: I3f8b6a88258c07d78964dd455fb9f99f65266301