Include base.h in tool/internal.h.

This is attempting to fix a Windows build failure when building args.cc.

Change-Id: I6e0c05303832c446d07e5e0d95a1c5151d275788

tool/internal.h

diff --git a/tool/internal.h b/tool/internal.h
index eae8881..84f8c4d 100644
--- a/tool/internal.h
+++ b/tool/internal.h
@@ -15,6 +15,8 @@
 #ifndef OPENSSL_HEADER_TOOL_INTERNAL_H
 #define OPENSSL_HEADER_TOOL_INTERNAL_H
 
+#include <openssl/base.h>
+
 #include <string>
 #include <vector>