Function execfuncdef 

pub fn execfuncdef(state: &mut estate, redir_prog: Option<Eprog>) -> i32

Port of execfuncdef() from Src/exec.c:5309 — C decl execfuncdef(Estate state, Eprog redir_prog). Define a shell function: extract name(s)+body from the wordcode payload, allocate the Shfunc, install into shfunctab (named), or execute immediately (anon).