Customizable seed collection and script improvements

[HazyFish]

• support multi-component triple, attrs, cpu everywhere
• support more customizable seed collection to ignore parts of triple, cpu, and/or attrs
• use consistent names, values, and data structure everywhere
  • target consists of triple, cpu, attrs
  • use LLVM C API to normalize triple
  • triple contains arch, vendor, os, abi
  • differentiate backend (e.g. "X86") and arch (e.g. "x86_64", "i686")
  • consistently use env vars
• update target list
• break down common.py and some other long scripts into multiple files in lib folder