Disable threads as it seems to trigger funky bugs. Enable it on all
archs but sparc64 as it's broken there.
Testing on arm/mips64el by kili, sparc64/ppc by me.
all secondary compilers were relocated to separate projects so we need a
rakudo port to get the perl6 binary back.
this update also addresses the recent bulk fallout noticed by naddy@
testing by sthen@ and ajacoutot@, thanks!