Remove some usage of SIZEOF*

- Remove MacOS hack in src/config.h.cmakein. It wasn't described in detail why
  it was needed. Removed with the asssumption that new cmake versions don't
  have that problem anymore.
- Require 64bit file support. There is no need to keep 32bit file support, now
  that we require 64bit integer. And remove unnessary code.

Change-Id: I501d8b8430ec93ada415b9ac0b60ba6d095c4725