Remove unneeded PC restore in vm_growstack_*.
Don't declare symbols that are unused in interpreter-only builds.
Don't embed lj_vm_foldfpm in interpreter-only builds.
Add 2nd temporary TValue in lua_State.
Drop call gates. Use function headers, dispatched like bytecodes.
Emit BC_FUNCF/BC_FUNCV bytecode at PC 0 for all Lua functions.
C functions and ASM fast functions get extra bytecodes.
Modify internal calling convention: new base in BASE (formerly in RA).
Can now use better C function wrapper semantics (dynamic on/off).
Prerequisite for call hooks with zero-overhead if disabled.
Prerequisite for compiling recursive calls.
Prerequisite for efficient 32/64 bit prototype guards.
Make external unwinding the default on x64.
It's mandatory on WIN64 due to the abundance of callee-saved regs.
Allow piecewise internal frame unwinding and optional cleanup.
Store ERRMEM, ERRERR and ERRCPP early and copy down later.
Use FRAME_CP for lj_vm_resume.
Add lj_vm_unwind_*_eh variants as landing pads for external unwinder.
Use fastcall for lj_vm_unwind_*.
Can drop r12/r13 saves in POSIX/x64 interpreter now.
Get number of multiple results from C frame.
Add lj_cont_hook: restores multres and dispatch to static ins.
Can use fastcall for lj_dispatch_ins() now.
