dash: fix build with musl

musl libc requires the getopt.h header for the definition of 'optreset'.

Fixes:
http://autobuild.buildroot.net/results/c23/c233ade479d6124ed7b382f2aa9859fe509d7bca/
http://autobuild.buildroot.net/results/081/0813c13c2a978316e6fa9a3cdbd5512612f5c374/
http://autobuild.buildroot.net/results/182/18230384d8225fbd7fddabfcbd685eaa38e31b31/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/dash/0002-histedit-fix-build-with-musl-libc.patch

@@ -0,0 +1,35 @@
+From 2da5b72c704fed10f1b04b5432ac6b078d016fae Mon Sep 17 00:00:00 2001
+From: Baruch Siach <baruch@tkos.co.il>
+Date: Fri, 2 Mar 2018 08:25:36 +0200
+Subject: [PATCH] histedit: fix build with musl libc
+
+musl libc defines the optreset BSD extension only in getopt.h. This
+fixes the following build failure:
+
+histedit.c: In function 'histcmd':
+histedit.c:220:2: error: 'optreset' undeclared (first use in this function)
+  optreset = 1; optind = 1; /* initialize getopt */
+  ^~~~~~~~
+
+Signed-off-by: Baruch Siach <baruch@tkos.co.il>
+---
+Upstream status: https://www.mail-archive.com/dash@vger.kernel.org/msg01389.html
+
+ src/histedit.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/src/histedit.c b/src/histedit.c
+index 94465d785cc9..f5c90aba873b 100644
+--- a/src/histedit.c
++++ b/src/histedit.c
+@@ -39,6 +39,7 @@
+ #include <stdio.h>
+ #include <stdlib.h>
+ #include <unistd.h>
++#include <getopt.h>
+ /*
+  * Editline and history functions (and glue).
+  */
+-- 
+2.16.1
+