Include output from `stack` when building from source

[hdgarrood]

Right now, whenever we fall back to building the compiler from source, we don't include the output from stack while building. This is very inconvenient if stack fails. For example, this can be seen in both #16 (comment) and in #21 (comment).

[jmatsushita]

Trying to build on a Jetson Nano (aarch64) in a Docker container (based on Debian Buster) and had to run stack setup to see the error indeed. Which in my case is:

Unable to find installation URLs for OS key: linux-aarch64-tinfo6

Which is reported here in this issue about stack dropping arm support but could be related to the ncurses version as reported here.

Update: In case someone else runs into the same problem, I could circumvent the issue by using an ubuntu:18.04 base image which allowed stack to find an aarch64 GHC bindist (since this version of ubuntu seems to use tinfo5).