These show gains from the recent optimization commits:
```
arg_splat
miniruby: 7346039.9 i/s
miniruby-before: 4692240.8 i/s - 1.57x slower
arg_splat_block
miniruby: 6539749.6 i/s
miniruby-before: 4358063.6 i/s - 1.50x slower
splat_kw_splat
miniruby: 5433641.5 i/s
miniruby-before: 3851048.6 i/s - 1.41x slower
splat_kw_splat_block
miniruby: 4916137.1 i/s
miniruby-before: 3477090.1 i/s - 1.41x slower
splat_kw_block
miniruby: 2912829.5 i/s
miniruby-before: 2465611.7 i/s - 1.18x slower
arg_splat_post
miniruby: 2195208.2 i/s
miniruby-before: 1860204.3 i/s - 1.18x slower
```
zsuper only speeds up in the post argument case, because
it was already set to use splatarray false in cases where
there were no post arguments.