Minor security cleanup

* `using` syntax is valid in all C++ versions, default to that.
* include the declaration for memset
diff --git a/src/lib/profiles/security/WeaveCert.h b/src/lib/profiles/security/WeaveCert.h
index 066f8e9..ee10c6d 100644
--- a/src/lib/profiles/security/WeaveCert.h
+++ b/src/lib/profiles/security/WeaveCert.h
@@ -26,6 +26,8 @@
 #ifndef WEAVECERT_H_
 #define WEAVECERT_H_
 
+#include <string.h>
+
 #include <Weave/Support/NLDLLUtil.h>
 #include <Weave/Core/WeaveTLV.h>
 #include <Weave/Support/ASN1.h>
diff --git a/src/lib/profiles/security/WeaveSig.h b/src/lib/profiles/security/WeaveSig.h
index bbb4314..9a37847 100644
--- a/src/lib/profiles/security/WeaveSig.h
+++ b/src/lib/profiles/security/WeaveSig.h
@@ -93,11 +93,7 @@
 
     WEAVE_ERROR GenerateSignature(const uint8_t * msgHash, uint8_t msgHashLen, TLVWriter & writer, uint64_t tag) __OVERRIDE;
 
-#if __cplusplus >= 201103L
     using WeaveSignatureGeneratorBase::GenerateSignature;
-#else
-    WeaveSignatureGeneratorBase::GenerateSignature;
-#endif
 
 private:
     virtual WEAVE_ERROR GenerateSignatureData(const uint8_t * msgHash, uint8_t msgHashLen, TLVWriter & writer) __OVERRIDE;