ash: parser: Fix single-quoted patterns in here-documents

Upstream commit:

    From: Herbert Xu <herbert@gondor.apana.org.au>
    Date: Fri, 9 Mar 2018 23:07:53 +0800
    parser: Fix single-quoted patterns in here-documents

    The script

            x=*
            cat <<- EOF
                    ${x#'*'}
            EOF

    prints * instead of nothing as it should.  The problem is that
    when we're in sqsyntax context in a here-document, we won't add
    CTLESC as we should.  This patch fixes it:

    Reported-by: Harald van Dijk <harald@gigawatt.nl>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash_test/ash-heredoc/heredoc_var_expand1.right

@@ -0,0 +1,4 @@
+
+Ok1:0
+
+Ok2:0

shell/ash_test/ash-heredoc/heredoc_var_expand1.tests

@@ -0,0 +1,11 @@
+x='*'
+
+cat <<- EOF
+	${x#'*'}
+EOF
+echo Ok1:$?
+
+cat <<EOF
+${x#'*'}
+EOF
+echo Ok2:$?