I'm trying to build the following repo as a library https://github.com/nomad-software/tcltk and it's failing like this:

C:\Users\gary\Desktop\tcltk>dub
Checking dependencies in 'C:\Users\gary\Desktop\tcltk'
Package tcltk (configuration "library") defines no main source file, this may cause certain build modes to fail. Add an explicit "mainSourceFile" to the package description to fix this.
Building configuration "library", build type debug
Running dmd...
.dub\build\library-debug-x86-dmd-DA39A3EE5E6B4B0D3255BFEF95601890AFD80709\tcltk.lib: Error: multiple definition of tcl_38_307: _Tcl_Main and Tcl_Main: _Tcl_Main
Error executing command run: DMD compile run failed with exit code 1

but then if i run the same command again, it builds

C:\Users\gary\Desktop\tcltk>dub
Checking dependencies in 'C:\Users\gary\Desktop\tcltk'
Package tcltk (configuration "library") defines no main source file, this may cause certain build modes to fail. Add an explicit "mainSourceFile" to the package description to fix this.
Target is up to date. Skipping build.
Target is a library. Skipping execution.

If this repo is a dependency on another project then this doesn't happen. It's only when i try to build it separately.

Any idea what's going on? I'm using Windows 7.