Fix compilation error: '_1' was not declared in this scope

Change-Id: I0f1f2df817a65f7d5b72c5280451346a0a011d47
diff --git a/lib/transmitter/gen_test_ab_impl.cc b/lib/transmitter/gen_test_ab_impl.cc
index 1ce3658..dc0fba7 100644
--- a/lib/transmitter/gen_test_ab_impl.cc
+++ b/lib/transmitter/gen_test_ab_impl.cc
@@ -62,7 +62,7 @@
         message_port_register_in(pmt::intern("bursts_in"));
         message_port_register_out(pmt::intern("bursts_out"));
 
-        set_msg_handler(pmt::intern("bursts_in"),  boost::bind(&gen_test_ab_impl::generate_ab,   this, _1));
+        set_msg_handler(pmt::intern("bursts_in"),  boost::bind(&gen_test_ab_impl::generate_ab,   this, boost::placeholders::_1));
     }
 
     /*
diff --git a/lib/transmitter/preprocess_tx_burst_impl.cc b/lib/transmitter/preprocess_tx_burst_impl.cc
index 5fbac98..2023ee6 100644
--- a/lib/transmitter/preprocess_tx_burst_impl.cc
+++ b/lib/transmitter/preprocess_tx_burst_impl.cc
@@ -55,7 +55,7 @@
         message_port_register_out(pmt::mp("bursts_out"));
 
         set_msg_handler(pmt::mp("bursts_in"),
-          boost::bind(&preprocess_tx_burst_impl::process_burst, this, _1));
+          boost::bind(&preprocess_tx_burst_impl::process_burst, this, boost::placeholders::_1));
     }
 
     /*
diff --git a/lib/transmitter/txtime_setter_impl.cc b/lib/transmitter/txtime_setter_impl.cc
index fecc498..8e6b3cf 100644
--- a/lib/transmitter/txtime_setter_impl.cc
+++ b/lib/transmitter/txtime_setter_impl.cc
@@ -76,10 +76,10 @@
         // Bind message handlers
         set_msg_handler(pmt::mp("fn_time"),
           boost::bind(&txtime_setter_impl::process_fn_time_reference,
-            this, _1));
+            this, boost::placeholders::_1));
         set_msg_handler(pmt::mp("bursts_in"),
           boost::bind(&txtime_setter_impl::process_txtime_of_burst,
-            this, _1));
+            this, boost::placeholders::_1));
     }
 
     /*