If constinit is not implemented by the compiler yet, fall back to constexpr.

src/CoreData/PrimitiveTypes.hpp

@@ -4,6 +4,10 @@
 #include <string>
 #include "Identifier.hpp"
 
+#if !__cpp_constinit
+#define constinit constexpr
+#endif
+
 namespace MalachScript {
     static constinit Identifier _voidName = u8"void";
     static constinit Identifier _intName = u8"int";