Add missing Blake2s source files

src/Crypto/blake2s_SSE2.c

@@ -0,0 +1,39 @@
+/*
+   BLAKE2 reference source code package - optimized C implementations
+
+   Copyright 2012, Samuel Neves <sneves@dei.uc.pt>.  You may use this under the
+   terms of the CC0, the OpenSSL Licence, or the Apache Public License 2.0, at
+   your option.  The terms of these licenses can be found at:
+
+   - CC0 1.0 Universal : http://creativecommons.org/publicdomain/zero/1.0
+   - OpenSSL license   : https://www.openssl.org/source/license.html
+   - Apache 2.0        : http://www.apache.org/licenses/LICENSE-2.0
+
+   More information about the BLAKE2 hash function can be found at
+   https://blake2.net.
+*/
+
+/* Adapted for VeraCrypt */
+
+#include "blake2.h"
+#include "Common/Endian.h"
+#include "Crypto/config.h"
+#include "Crypto/cpu.h"
+#include "Crypto/misc.h"
+
+#if CRYPTOPP_BOOL_SSE2_INTRINSICS_AVAILABLE
+
+#include "blake2s-round.h"
+
+int blake2s_has_sse2()
+{
+    return 1;
+}
+
+#else
+int blake2s_has_sse2()
+{
+    return 0;
+}
+
+#endif