work on JIT support

[nilslice]

Consider the following to improve performance:

• adding suggestions from @jart (anyone working on cosmopolitan ffmepg? jart/cosmopolitan#352 (reply in thread)) so WAMR can build in FastJIT mode on Cosmo.
• determine level of effort to add arm64 code gen for WAMR FastJIT... asmjit backend exists, would need to see if this is feasible and can be built on Cosmo too (targeting a single fat binary).

Benefits:

• would speed up code execution significantly
• SIMD support?

Drawbacks:

• larger binary size for all Hermits

[G4Vi]

Started work on FastJit. Linux works, but looks like other platforms need work. #32 Provides a 5X+ speed improvement for about 400k bytes, but does not add SIMD support.