Allow suppression of per binding Core stats

Motivation

Even with -dsuppress-all, -ddump-simpl adds Core stats to every top-level binding, e.g.:

-- RHS size: {terms: 12, types: 3, coercions: 0, joins: 0/0} <-- THIS
bitOrInt64
  = \ x ->
      case x of { I64# x# ->
      I64# (word2Int# (or# (or# (int2Word# x#) 250##) 175##))
      }

Proposal

Only enable Core stats when -ddump-core-stats is passed.