Ctrl + C does not terminate hadrian build.

This is a known issue. See also:

• https://github.com/ndmitchell/shake/issues/169
• https://github.com/mintty/mintty/issues/684
• https://github.com/snowleopard/hadrian/issues/696#

The best workaround for this I found so far was to use winpty:

eg:

winpty -- hadrian/build.bat -j4

It's part of the msys distribution so can be installed using:

pacman -S winpty