boehmgc: switch from versionAtLeast to == for powerpc workaround

  ++ lib.optional enableMmap "--enable-mmap"

  ++ lib.optional enableLargeConfig "--enable-large-config";

  # this stanza can be dropped when a release fixes this issue:

  # This stanza can be dropped when a release fixes this issue:

  #   https://github.com/ivmai/bdwgc/issues/376

  # The version is checked with == instead of versionAtLeast so we

  # don't forget to disable the fix (and if the next release does

  # not fix the problem the test failure will be a reminder to

  # extend the set of versions requiring the workaround).

  makeFlags = if (stdenv.hostPlatform.isPower64 &&

                  lib.versionAtLeast finalAttrs.version "8.2.2")

                  finalAttrs.version == "8.2.2")

    then [

      # do not use /proc primitives to track dirty bits; see:

      # https://github.com/ivmai/bdwgc/issues/479#issuecomment-1279687537