Include assert.h, don't rely on other headers including it.

Change-Id: I4486c4a23d28bf5412d5f90ca2eb0ec9cc0a5929
diff --git a/fuchsia/fuchsia-compat.c b/fuchsia/fuchsia-compat.c
index 40de8d8..f229b63 100644
--- a/fuchsia/fuchsia-compat.c
+++ b/fuchsia/fuchsia-compat.c
@@ -7,6 +7,7 @@
 #include <mxio/io.h>
 #include <pthread.h>
 #include <pwd.h>
+#include <assert.h>
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>