ash: use pgetc_eatbnl() in more places, take 3

Adding previously skipped "readtoken1(pgetc_eatbnl(), syntax_type..." change
from upstream commit:

    Date:   Thu Mar 8 08:37:11 2018 +0100
    parser: use pgetc_eatbnl() in more places

    dash has a pgetc_eatbnl function in parser.c which skips any
    backslash-newline combinations. It's not used everywhere it could be.
    There is also some duplicated backslash-newline handling elsewhere in
    parser.c. Replace most of the calls to pgetc() with calls to
    pgetc_eatbnl() and remove the duplicated backslash-newline handling.

Testcase:
	PS1='\
	:::'
should result in ::: prompt, not <newline>::: prompt

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

shell/ash.c

@@ -13388,7 +13388,7 @@ expandstr(const char *ps, int syntax_type)
 	 * PS1='$(date "+%H:%M:%S) > '
 	 */
 	exception_handler = &jmploc;
-	readtoken1(pgetc(), syntax_type, FAKEEOFMARK, 0);
+	readtoken1(pgetc_eatbnl(), syntax_type, FAKEEOFMARK, 0);
 
 	n.narg.type = NARG;
 	n.narg.next = NULL;