Panic from ghc-stage1 when building HEAD with profiling

When building 3a18baff with profiling, GHC emits this error:

ghc-stage1: panic! (the 'impossible' happened)
  (GHC version 8.1.20170106 for x86_64-unknown-linux):
	kindPrimRep.go
  k0
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable
        pprPanic, called at compiler/simplStg/RepType.hs:369:9 in ghc:RepType

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

compiler/ghc.mk:582: recipe for target 'compiler/stage2/build/StgCmmMonad.p_o' failed

I have attached my build.mk file. It may be wrong, but I don't think it includes anything that should break GHC. Even if it did, I should get some sort of error message, not a panic.

The bootstrap compiler is GHC 8.0.1, built from the ghc-8.0.1-release tag in the Git repository.