fix some none portable code that was using GCC impl details

src/InternalDHKeyExchange.cc

@@ -68,10 +68,18 @@ void DHKeyExchange::init(const unsigned char* prime, size_t primeBits,
   generator_ = n(gen.c_str(), gen.length());
 
   size_t pbytes = (privateKeyBits + 7) / 8;
+#if defined(_MSC_VER)
+  // MSVC will not compile dynamic arrays
+  unsigned char* buf = new unsigned char[pbytes];
+#else
   unsigned char buf[pbytes];
+#endif
   util::generateRandomData(buf, pbytes);
   privateKey_ = n(reinterpret_cast<char*>(buf), pbytes);
-
+#if defined(_MSC_VER)
+  // clean up memory
+  delete[] buf;
+#endif
   keyLength_ = (primeBits + 7) / 8;
 }
 

src/SocketRecvBuffer.cc

@@ -51,7 +51,7 @@ SocketRecvBuffer::~SocketRecvBuffer() = default;
 
 ssize_t SocketRecvBuffer::recv()
 {
-  size_t n = std::end(buf_) - last_;
+  size_t n = (buf_.data() + 16_k) - last_;
   if (n == 0) {
     A2_LOG_DEBUG("Buffer full");
     return 0;