ash: expand: Merge syntax/quotes in memtodest with flags

ash: expand: Merge syntax/quotes in memtodest with flags

Upstream commit:

    Date: Mon, 28 May 2018 00:17:39 +0800
    expand: Merge syntax/quotes in memtodest with flags

    The function arguments syntax and quotes are both derived from
    the expansion flags.  As syntax is only used by memtodest we do
    not need to maintain it outside of the function at all.

    The only place that uses something other than BASESYNTAX or DQSYNTAX
    is exptilde.  However in that case DQSYNTAX has exactly the same
    effect as SQSYNTAX.

    This patch merges these two arguments into a single flags.  The
    macro QUOTES_KEEPNUL has been renamed to EXP_KEEPNUL in order
    to keep the namespace separate.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>