Fix compatibility with boost-1.73+

Backport of https://github.com/PowerDNS/pdns/commit/71246536642590e8e8b21c11307ec4bd0e165066

--- a/pdns/ixfrdist-web.cc
+++ b/pdns/ixfrdist-web.cc
@@ -32,7 +32,7 @@ IXFRDistWebServer::IXFRDistWebServer(const ComboAddress &listenAddress, const Ne
 {
   d_ws->setACL(acl);
   d_ws->setLogLevel(loglevel);
-  d_ws->registerWebHandler("/metrics", boost::bind(&IXFRDistWebServer::getMetrics, this, _1, _2));
+  d_ws->registerWebHandler("/metrics", std::bind(&IXFRDistWebServer::getMetrics, this, std::placeholders::_1, std::placeholders::_2));
   d_ws->bind();
 }
 
--- a/pdns/webserver.cc
+++ b/pdns/webserver.cc
@@ -107,7 +107,7 @@ static void bareHandlerWrapper(WebServer::HandlerFunction handler, YaHTTP::Reque
 
 void WebServer::registerBareHandler(const string& url, HandlerFunction handler)
 {
-  YaHTTP::THandlerFunction f = boost::bind(&bareHandlerWrapper, handler, _1, _2);
+  YaHTTP::THandlerFunction f = std::bind(&bareHandlerWrapper, handler, std::placeholders::_1, std::placeholders::_2);
   YaHTTP::Router::Any(url, f);
 }
 
@@ -179,7 +179,7 @@ void WebServer::apiWrapper(WebServer::HandlerFunction handler, HttpRequest* req,
 }
 
 void WebServer::registerApiHandler(const string& url, HandlerFunction handler, bool allowPassword) {
-  HandlerFunction f = boost::bind(&WebServer::apiWrapper, this, handler, _1, _2, allowPassword);
+  HandlerFunction f = std::bind(&WebServer::apiWrapper, this, handler, std::placeholders::_1, std::placeholders::_2, allowPassword);
   registerBareHandler(url, f);
 }
 
@@ -196,7 +196,7 @@ void WebServer::webWrapper(WebServer::HandlerFunction handler, HttpRequest* req,
 }
 
 void WebServer::registerWebHandler(const string& url, HandlerFunction handler) {
-  HandlerFunction f = boost::bind(&WebServer::webWrapper, this, handler, _1, _2);
+  HandlerFunction f = std::bind(&WebServer::webWrapper, this, handler, std::placeholders::_1, std::placeholders::_2);
   registerBareHandler(url, f);
 }
 
--- a/pdns/ws-auth.cc
+++ b/pdns/ws-auth.cc
@@ -2328,8 +2328,8 @@ void AuthWebServer::webThread()
       d_ws->registerApiHandler("/api", &apiDiscovery);
     }
     if (::arg().mustDo("webserver")) {
-      d_ws->registerWebHandler("/style.css", boost::bind(&AuthWebServer::cssfunction, this, _1, _2));
-      d_ws->registerWebHandler("/", boost::bind(&AuthWebServer::indexfunction, this, _1, _2));
+      d_ws->registerWebHandler("/style.css", std::bind(&AuthWebServer::cssfunction, this, std::placeholders::_1, std::placeholders::_2));
+      d_ws->registerWebHandler("/", std::bind(&AuthWebServer::indexfunction, this, std::placeholders::_1, std::placeholders::_2));
     }
     d_ws->go();
   }