Alias/heredoc/cmdsubst regression

[Martijn Dekker <martijn@inlv.org>]

There is a regression involving alias expansion, a here-document, and a 
command substitution. The following worked fine until dash 0.5.8; it 
throws a syntax error as of dash 0.5.9.

alias BEGIN='{' END='}'
BEGIN
cat <<eof
$(echo hi)
eof
END

With some git brute-forcing I determined this was the commit that broke it:

> commit 7c245aa8ed33ba5db30eef9369d67036a05b0371
> Author: Herbert Xu <herbert@gondor.apana.org.au>
> Date:   Tue Oct 28 17:22:16 2014 +0800
> 
>     [PARSER] Simplify EOF/newline handling in list parser
> 
>     This patch simplifies the EOF and new handling in the list parser.
>     In particular, it eliminates a case where we may leave here-documents
>     unfinished upon EOF.
> 
>     It also removes special EOF/newline handling from parsecmd.

Related shells:
- I've confirmed the test case to work fine on:
	FreeBSD sh 9, 10, 11 and 12
	NetBSD sh 8 and 9.0RC1
	busybox ash 1.20 - 1.24
- I've confirmed the test case broken on:
	busyboxy ash 1.25 through current

Since busybox ash tracks dash, it's not surprising it broke there as well.

- M.

-- 
modernish -- harness the shell
https://github.com/modernish/modernish