Fix <memory.h> to be a synonym for <string.h> like in glibc.

Change-Id: If23589c5d85dffd28788e04b010303620fa178ca
diff --git a/libc/include/memory.h b/libc/include/memory.h
index e69de29..3b2f590 100644
--- a/libc/include/memory.h
+++ b/libc/include/memory.h
@@ -0,0 +1 @@
+#include <string.h>