[optimizing compiler] Add support for volatile

- for backends: arm, x86, x86_64
- added necessary instructions to assemblies
- clean up code gen for field set/get
- fixed InstructionDataEquals for some instructions
- fixed comments in compiler_enums

* 003-opcode test verifies basic volatile functionality

Change-Id: I144393efa312dfb2c332cb84056b00edffee338a