html-xml-utils: fix musl build

srcpkgs/html-xml-utils/patches/musl.patch

@@ -0,0 +1,10 @@
+--- hxnum.c.orig	2016-03-20 16:18:47.815855780 +0100
++++ hxnum.c	2016-03-20 16:19:40.197200923 +0100
+@@ -29,6 +29,7 @@
+ #endif
+ #include <stdlib.h>
+ #include <assert.h>
++#include <getopt.h>
+ #include "export.h"
+ #include "types.e"
+ #include "class.e"