Revert "Disable reedsolomon per #1279"
Revert "Disable reedsolomon per #1279"

Re-enable the `reedsolomon` package, but disable the `llvm` Cabal flag:
the Stackage build servers run a version of LLVM that's incompatible
with the GHC version being used, causing the build to fail when the
`llvm` flag (which passes `-fllvm` to GHC) is enabled.

This reverts commit 10a218a8436290ca4e962bcea5d6e18e4e291917.

Conflicts:
	build-constraints.yaml

Fixes: fpco/stackage#1279
See: https://github.com/fpco/stackage/issues/1279

christiaanb/stackage,stackbuilders/stackage,Shimuuar/stackage,soenkehahn/stackage,int-index/stackage,judah/stackage,simonmichael/stackage,fimad/stackage,spencerjanssen/stackage,wereHamster/stackage,bartavelle/stackage,mgajda/stackage,creichert/stackage,alanz/stackage,k0ral/stackage,l29ah/stackage,jaspervdj/stackage,athanclark/stackage,agrafix/stackage,codedmart/stackage,iand675/stackage,marcinmrotek/stackage,garetxe/stackage,Daniel-Diaz/stackage,Gabriel439/stackage,brendanhay/stackage,lwm/stackage,ethercrow/stackage,mstksg/stackage,clinty/stackage,ygale/stackage,michalkonecny/stackage,DanielG/stackage,jonschoning/stackage,fpco/stackage,phaazon/stackage,asr/stackage,peti/stackage,GregorySchwartz/stackage,massysett/stackage,nomeata/stackage,phadej/stackage,mrkkrp/stackage