[pkg-go] Bug#792053: Bug#792053: Bug#792053: Bug#792053: prometheus: FTBFS w/ test suite errors

[Martín Ferrari]

Upstream has been very helpful digging into this issue. We have been
able to pin this down to a difference in the go compiler. If I use
upstream's Makefile to download the go runtime from golang.org and then
use that to build the package, the errors go away.

Now, it might not actually be a bug in the compiler, as this seems it
could be related to undefined behaviour when casting to unsigned values
(the upstream bug has more details).

-- 
Martín Ferrari (Tincho)