Define ConstantData::PoisonValue. Add support for poison value to LLLexer/LLParser/BitcodeReader/BitcodeWriter. Add support for poison value to llvm-c interface. Add support for poison value to OCaml binding. Add m_Poison in PatternMatch. Lower poison as undef in SelDag, GlobalISel and FastISel.

Define ConstantData::PoisonValue. Add support for poison value to LLLexer/LLParser/BitcodeReader/BitcodeWriter. Add support for poison value to llvm-c interface. Add support for poison value to OCaml binding. Add m_Poison in PatternMatch.

Define ConstantData::PoisonValue. Add support for poison value to LLLexer/LLParser/BitcodeReader/BitcodeWriter. Add support for poison value to llvm-c interface. Add support for poison value to OCaml binding. Add m_Poison in PatternMatch. Lower poison as undef in SelDag, GlobalISel and FastISel.