xar: fix -Wimplicit-function-declaration

srcpkgs/xar/patches/implicit-function-decl.patch

@@ -0,0 +1,20 @@
+--- a/xar/lib/ext2.c
++++ b/xar/lib/ext2.c
+@@ -41,6 +41,7 @@
+ #include "asprintf.h"
+ #endif
+ #include <stdio.h>
++#include <stdlib.h>
+ #include <unistd.h>
+ #include "xar.h"
+ #include "arcmod.h"
+--- a/xar/lib/linuxattr.c
++++ b/xar/lib/linuxattr.c
+@@ -37,6 +37,7 @@
+ 
+ #include "config.h"
+ #include <stdio.h>
++#include <stdlib.h>
+ #include <unistd.h>
+ #include <libgen.h>
+ #include "xar.h"