chisel-torture: A Chisel fuzz tester


The following bugs have been found using chisel-torture:

In chisel:
  fdcac4e Fix long RSH by adding dat_t::operator[](size_t)
  15f3035 Fix a code-gen issue related to reinterpret_cast
  855ad54 Remove a spurious newline from Flo's log2 generation rule
  2f508fe Mark mod_api_t::string_comparator::() as const

In flo-llvm:
  18ba6f2 Fix a LSH width odditity