install: stop building on build failures

[tibbe]

Today, we continue building packages even if one failed to build. It's this way because once upon a time @dcoutts was building all of Hackage and keeping building on failure made sense then. @dcoutts and I agree that this probably not the right default so we should

• stop building on failure (when using parallel builds some packages may already be in-flight, that's OK),
• add a --keep-going flag that enables the old behavior.

[ttuegel]

Because we now print the whole build log, continuing to install packages can push the build log out of scrollback, which makes this even more problematic.

[reinh]

👍, I think failing early would be the sensible default.