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>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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).
  */