cast to pure function stop work after upgrade

[baby_tiger]

this used work for me, after upgrade I get this error.  how to 
fix it ?


     import std.traits;
             enum LogLevel : ubyte {
                     INFO = 0,
                     WARN,
                     ERROR,
                     FATAL,
             }


     extern (C) string VFORMAT(LogLevel level, string file, size_t 
line, char[] tmp, bool line_break, string tag, string fmt, ...) 
@nogc nothrow {
             return null;
     }

     template asPure(string P, alias Fn) if 
(isFunctionPointer!(typeof(&Fn))) {
             enum N = __traits(identifier, Fn);
             enum string asPure = "private alias " ~ N ~ "_PURE = 
" ~ typeof(&Fn).stringof ~ " pure;\n" ~ "__gshared immutable " ~ 
N ~ "_PURE " ~ P ~"= cast(" ~ N ~ "_PURE) &" ~ N ~ " ;" ;
     }
     enum xx = asPure!("VFORMATP", VFORMAT);
     mixin(xx);

void main(){

}


      reinterpreting cast from `nothrow @nogc extern (C) 
string(LogLevel level, string file, ulong line, char[] tmp, bool 
line_break, string tag, string fmt, ...)*` to `pure nothrow @nogc 
extern (C) string(LogLevel, string, ulong, char[], bool, string, 
string, ...)*` is not supported in CTFE