Function execfuncdef 

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

Port of execfuncdef(Estate state, Eprog redir_prog) from Src/exec.c:5309-5494. Define a shell function: extract name(s)+body from the wordcode payload, allocate the Shfunc, install into shfunctab (named), or execute immediately (anon).