mixin under -betterC

[DLearner via Digitalmars-d-learn]

Code below is intended to test simple mixin with lambda function 
under -betterC.
Works with full-D, but fails with 'needs GC' errors under 
-betterC.

Why is this so, bearing in mind the concatenations are executed at
compile, not run, time?
```
// Test harness
   extern(C) void main() {
      import core.stdc.stdio : printf;
      import testmod;

      bool FirstVarGreater;
      int Var_A = 4;
      int Var_B = 3;


      FirstVarGreater = mixin(mxnTest("Var_A", "Var_B"));
      if (FirstVarGreater) {
            printf("First Var is Greater\n");
      } else {
            printf("First Var is not Greater\n");
      }
   }


// testmod

string mxnTest(string strVar1, string strVar2) {
   return `(int Var1, int Var2) {
      if (Var1 > Var2) {
         return true;
      } else {
         return false;
      }
   }(` ~ strVar1 ~ `,` ~ strVar2 ~ `)`;
}
```