x86: coalesce reference and int entry points into vtos bytecodes

On x86 - both 32- and 64-bit, the code laid out for transitionining into a vtos bytecode when having a reference and int top-of-stack state is semantically identical, and can be coalesced:

https://github.com/openjdk/jdk/compare/master...cl4es:atos_itos_opt

This removes a short jump on some cases which is marginally beneficial when interpreting, while measurably reducing overhead of generating the interpreter itself