C++20 fixes

Fix compilation with gcc13 / c++20 , ROOT 6.28.04 (LCG dev4), fmtlib 10.0.0

• use fmt::runtime where needed (with a hack to still work with fmtlib < 8)
• avoid implicit capture of this in lambdas via [=]
• fix comparison between Gaudi::Property<std::string> and const char*
• hide std::source_location to cling

Closes #266 (closed)

GaudiCoreSvc/src/MessageSvc/MessageSvcSink.cpp

@@ -105,18 +105,20 @@ public:
       assert( entry != registry.end() );
       // print the json string according to format found
       // This actually will call this formatter again a number of times
-      return fmt::format_to( ctx.out(), entry->second, json_arg );
+      return fmt::format_to( ctx.out(), fmt::runtime( entry->second ), json_arg );
     } else {
       // dealing with a {:name|fmt} format
-      auto actualFormat = fmt::format( "{{:{}", currentFormat ) + "}";
+      auto actualFormat = fmt::format( "{{:{}", fmt::runtime( currentFormat ) ) + "}";
       switch ( currentFormat.back() ) {
       case 'd':
-        return fmt::format_to( ctx.out(), actualFormat, j.at( currentName ).template get<unsigned int>() );
+        return fmt::format_to( ctx.out(), fmt::runtime( actualFormat ),
+                               j.at( currentName ).template get<unsigned int>() );
       case 'g':
-        return fmt::format_to( ctx.out(), actualFormat, j.at( currentName ).template get<double>() );
+        return fmt::format_to( ctx.out(), fmt::runtime( actualFormat ), j.at( currentName ).template get<double>() );
       case 'p':
         actualFormat[actualFormat.size() - 2] = 'g';
-        return fmt::format_to( ctx.out(), actualFormat, j.at( currentName ).template get<double>() * 100 );
+        return fmt::format_to( ctx.out(), fmt::runtime( actualFormat ),
+                               j.at( currentName ).template get<double>() * 100 );
       default:
         return fmt::format_to( ctx.out(), "Unknown counter format : {}", currentFormat );
       }