security: New --without-osx-keychain option to disable use of OSX Keychain as a default TPM on Darwin platform

Change-Id: I9f8dcab585ef4d4c00a0687d92001eec1919632a
diff --git a/src/security/key-chain.hpp b/src/security/key-chain.hpp
index 86589eb..ca732d8 100644
--- a/src/security/key-chain.hpp
+++ b/src/security/key-chain.hpp
@@ -476,7 +476,7 @@
 
 
 
-#ifdef NDN_CPP_HAVE_OSX_SECURITY
+#if defined(NDN_CPP_HAVE_OSX_SECURITY) and defined(NDN_CPP_WITH_OSX_KEYCHAIN)
 
 namespace ndn
 {