Add missing includes in compat implementation

These includes are necessary for the strdup() compat implementation.

app/src/compat.c

@@ -2,6 +2,9 @@
 
 #include "config.h"
 
+#include <stdlib.h>
+#include <string.h>
+
 #ifndef HAVE_STRDUP
 char *strdup(const char *s) {
     size_t size = strlen(s) + 1;