Portable bit functions
Portable bit functions

As discussed here:
  https://github.com/WebAssembly/binaryen/pull/34#discussion_r48379297

It's useful to have portable bit functions instead of relying on compiler builtins which aren't always portable.

WebAssembly/binaryen,yurydelendik/binaryen,WebAssembly/binaryen,yurydelendik/binaryen,yurydelendik/binaryen,ddcc/binaryen,ddcc/binaryen,WebAssembly/binaryen,yurydelendik/binaryen,yurydelendik/binaryen,ddcc/binaryen,WebAssembly/binaryen,ddcc/binaryen,WebAssembly/binaryen,ddcc/binaryen