Ruby

Fix keyword argument separation issues with sym procs when using refinements

Make sure that vm_yield_with_cfunc can correctly set the empty keyword
flag by passing 2 as the kw_splat value when calling it in
vm_invoke_ifunc_block. Make sure calling.kw_splat is set to 1 and not
128 in vm_sendish, so we can safely check for different kw_splat values.

vm_args.c needs to call add_empty_keyword, and to make JIT happy, the
function needs to be exported. Rename the function to
rb_adjust_argv_kw_splat to more accurately reflect what it does, and
mark it as MJIT exported.