Failed to link a 7 month old GTKD project

[Ki Rill]

I was updating my old D projects. Surprisingly... or not, I found 
one that outputs a linker error. Though, I clearly remember it 
compiled perfectly fine the last time I worked on it. It is a 
GTKD project using DUB.

DUB output:
```
Linking...
Undefined symbols for architecture x86_64:
   "__D3std4file11DirIterator15__fieldPostblitMFNaNbNiNlZv", 
referenced from:
       
__D3std9algorithm9iteration__T6filterS3app7listdirFAyaZ9__lambda2Z__TQBnTSQCt4file11DirIteratorZQCoMFQBcZSQDzQDyQDr__T12FilterResultSQDrQDqFQDlZQDlTQCxZQBi in extension-er.o
       
__D3std9algorithm9iteration__T12FilterResultS3app7listdirFAyaZ9__lambda2TSQCt4file11DirIteratorZQCo6__ctorMFNcQBlZSQEiQEhQEa__TQDtSQDiQDhFQDcZQDcTQCvZQEq in extension-er.o
       
__D3std9algorithm9iteration__T12FilterResultS3app7listdirFAyaZ9__lambda2TSQCt4file11DirIteratorZQCo6__ctorMFNcQBlbZSQEjQEiQEb__TQDuSQDjQDiFQDdZQDdTQCwZQEr in extension-er.o
       
__D3std9algorithm9iteration__T12FilterResultS3app7listdirFAyaZ9__lambda2TSQCt4file11DirIteratorZQCo15__fieldPostblitMFNaNbNiNlZv in extension-er.o
       __D32TypeInfo_S3std4file11DirIterator6__initZ in 
extension-er.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to 
see invocation)
Error: linker exited with status 1
```

If I'm not mistaken, this cryptic message tries to tell me that 
something is wrong with the standard library functions: 
`Undefined symbols...` But what's wrong exactly?

Any directions?

Any help solving this issue is greatly appreciated.