 Can't reproduce this with Debian version of astromenance neither with radeonsi
or swrast - works fine here with that llvm+mesa version.

 Likely game bug or it need some patches on Arch, look at a Debian changelog
there are some patching involved:

http://metadata.ftp-master.debian.org/changelogs//contrib/a/astromenace/astromenace_1.3.2+repack-3_changelog