`foo(*rest, post, **empty_kw)` is compiled like
`foo(*rest + [post, **empty_kw])`, and `**empty_kw` is removed by
"newarraykwsplat" instruction.
However, the method call still has a flag of KW_SPLAT, so "post" is
considered as a keyword hash, which caused a segfault.
Note that the flag cannot be removed if "empty_kw" is not always empty.

This change fixes the issue by compiling arguments with "newarray"
instead of "newarraykwsplat".

[Bug #16442]