[lldb] Fix warning: 'sprintf' is deprecated in RNBSocketTest

Fixes warning: 'sprintf' is deprecated: This function is provided for
compatibility reasons only.  Due to security concerns inherent in the
design of sprintf(3), it is highly recommended that you use snprintf(3)
instead.

Author: JDevlieghere

lldb/unittests/debugserver/RNBSocketTest.cpp

@@ -26,8 +26,8 @@ std::string goodbye = "Goodbye!";
 static void ServerCallbackv4(const void *baton, in_port_t port) {
   auto child_pid = fork();
   if (child_pid == 0) {
-    char addr_buffer[256];
-    sprintf(addr_buffer, "%s:%d", (const char *)baton, port);
+    std::string addr_buffer =
+        llvm::formatv("{0}:{1}", (const char *)baton, port).str();
     llvm::Expected<std::unique_ptr<Socket>> socket_or_err =
         Socket::TcpConnect(addr_buffer);
     ASSERT_THAT_EXPECTED(socket_or_err, llvm::Succeeded());
@@ -59,15 +59,12 @@ void TestSocketListen(const char *addr) {
   if (addresses.size() == 0)
     return;
 
-  char addr_wrap[256];
-  if (addresses.front().GetFamily() == AF_INET6)
-    sprintf(addr_wrap, "[%s]", addr);
-  else
-    sprintf(addr_wrap, "%s", addr);
+  const char *fmt = addresses.front().GetFamily() == AF_INET6 ? "[{0}]" : "{0}";
+  std::string addr_wrap = llvm::formatv(fmt, addr).str();
 
   RNBSocket server_socket;
-  auto result =
-      server_socket.Listen(addr, 0, ServerCallbackv4, (const void *)addr_wrap);
+  auto result = server_socket.Listen(addr, 0, ServerCallbackv4,
+                                     (const void *)addr_wrap.c_str());
   ASSERT_TRUE(result == rnb_success);
   result = server_socket.Write(hello.c_str(), hello.length());
   ASSERT_TRUE(result == rnb_success);
@@ -94,11 +91,9 @@ void TestSocketConnect(const char *addr) {
   if (addresses.size() == 0)
     return;
 
-  char addr_wrap[256];
-  if (addresses.front().GetFamily() == AF_INET6)
-    sprintf(addr_wrap, "[%s]:0", addr);
-  else
-    sprintf(addr_wrap, "%s:0", addr);
+  const char *fmt =
+      addresses.front().GetFamily() == AF_INET6 ? "[{0}]:0" : "{0}:0";
+  std::string addr_wrap = llvm::formatv(fmt, addr).str();
 
   Socket *server_socket;
   llvm::Expected<std::unique_ptr<Socket>> socket_or_err =