ash: eval: Only restore exit status on exit/return

ash: eval: Only restore exit status on exit/return

Upstream commit:

    Date: Fri, 14 Dec 2018 13:52:02 +0800
    eval: Only restore exit status on exit/return

    We unconditionally restore the saved status in exitreset, which
    is incorrect as we only want to do it for exitcmd and returncmd.
    This patch fixes the problem by introducing EXEND.

    Reported-by: Martijn Dekker <martijn@inlv.org>
    Fixes: da30b4b78769 ("[BUILTIN] Exit without arguments in a trap...")
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>