[optimizing compiler] Add div-int and exception handling.

- for backends: arm, x86, x86_64
- fixed a register allocator bug: the request for a fixed register for
the first input was ignored if the output was kSameAsFirstInput
- added divide by zero exception
- more tests
- shuffle around some code in the builder to reduce the number of lines
of code for a single function.

Change-Id: Id3a515e02bfbc66cd9d16cb9746f7551bdab3d42