Windows: rake build aborts

[AndyGauge]

I installed ruby 2.4 using https://medium.com/ruby-on-rails-web-application-development/how-to-install-rubyonrails-on-windows-7-8-10-complete-tutorial-2017-fc95720ee059
msys2 with pacman -S base-devel mingw-w64-x86_64-toolchain
rustc --version 1.23.0-nightly

rake build returns
HelixRuntime::MissingDllError: Unable to find helix-runtime-0-7-2.dll in $PATH.

I have c:\ruby24-x64\lib\ruby\gems\2.4.0\helix_runtime-0.7.3\ext\helix_runtime\native that includes .rb, .c .h, .o, .so, a Makefile, but no dlls anywhere.

It can create the crate using the rails generate helix: