gtkspell3 substitution failure--also, format of error message

Hi,

I get the following on guix package -u . with guix describe being

Generation 56 Feb 24 2020 16:19:39 (current)

guix eab07e7

repository URL: https://git.savannah.gnu.org/git/guix.git

branch: master

commit: eab07e78b691ae7866267fc04d31c7c3ad6b0eeb

guix substitute: error: host name lookup error: Name or service not known

substitution of /gnu/store/21kizyzrfh0ysh1ihhzngcy9ysvlq4dy-gtkspell3-3.0.9 failed

killing process 19078

killing process 19078: No such process

guix package: error: some substitutes for the outputs of derivation `/gnu/store/d18cxxd362rird73cylak2l7m3gzrz0i-gtkspell3-3.0.9.drv' failed (usually happens due to networking issues); try `--fallback' to build derivation from source

Maybe we should improve the error message to also print the name of the host

that Guix was trying to resolve.

./guix/scripts/substitute.scm: (leave (G_ "host name lookup error: ~a~%")