Without this fix, trying to use `scanTuple` in a generic proc imported
from a different module fails to compile (`undeclared identifier:
'scanf'`):
```nim
# module.nim
import std/strscans
proc scan*[T](s: string): (bool, string) =
s.scanTuple("$+")
```
```nim
# main.nim
import ./module
echo scan[int]("foo")
```
Workaround is to `export scanf` in `module.nim` or `import std/strscans`
in `main.nim`.
f8294ce06e