fix(build): fix compilation errors when using newer version of g++

Signed-off-by: Raphael Defosseux <raphael.defosseux@openairinterface.org>

src/pcf_app/pcf_client.hpp

@@ -47,7 +47,7 @@ class pcf_client {
   pcf_client(pcf_client const&) = delete;
   static long curl_http_client(
       std::string remoteUri, std::string method, std::string& response,
-      std::string msgBody = {});
+      std::string msgBody);
 };
 }  // namespace app
 }  // namespace pcf

src/pcf_app/pcf_nrf.cpp

@@ -42,7 +42,7 @@
 using namespace oai::pcf::app;
 using namespace oai::pcf::config;
 using namespace oai::pcf::model;
-
+using namespace boost::placeholders;
 using namespace std;
 
 extern pcf_nrf* pcf_nrf_inst;