Fix the build. (#483)

Author: rmpowell77

src/CalChartDoc.cpp

@@ -34,7 +34,6 @@
 #include "platconf.h"
 #include "print_ps.h"
 
-#include <format>
 #include <fstream>
 #include <iomanip>
 #include <wx/textfile.h>
@@ -220,9 +219,10 @@ T& CalChartDoc::LoadObjectGeneric(T& stream)
                 return ContinuityEditorPopup::ProcessEditContinuity(GetDocumentWindow(), description, what, line, column).ToStdString();
             },
             [this, &modified](int majorVersion, int minorVersion) {
-                auto message = std::format(
+                wxString message;
+                message.Printf(
                     "Warning: Current version of CalChart is older than show file.\n"
-                    "Current Version {}.{}, show file: {}.{}.\n"
+                    "Current Version %d.%d, show file: %d.%d.\n"
                     "Please consider upgrade to a newer version of CalChart by checking https://sourceforge.net/projects/calchart.\n"
                     "Continue trying to open this file?",
                     CC_MAJOR_VERSION,