build.sh: Mention troublesome repo in die() messages

So folks don't have to scroll back up and find the "build repo
${REPO}" message or similar.

Also wrap long lines after the '||' to try and stay in the vicinity of
80 characters ;).

The inspiration came from Erik's gentoo-bb commit [1].

[1]: https://github.com/edannenberg/gentoo-bb/blob/e653d78fdb17f218aec83b5b0e11c5bf2aa07253/build.sh#L246

Based-on-patch-by: Erik Dannenberg <erik.dannenberg@bbe-consulting.de>