Fix CMake 3.0 warning about policy CMP0043

Version 3.0 of CMake introduced policy CMP0043 which makes CMake ignore COMPILE_DEFINITIONS suffixed variables (they are to be set using generator expressions now instead, which can be done since version 2.8.10).

I was going to push/pop the policy as needed, but there's no reason to do so. We shouldn't really mix the old and new behaviors (there's only 6 places in OCE that need fixing), but aside from that, we can't use the new behavior anyway unless we bump the minimum required version to 2.8.10. The presence of this policy requires it to be set one way or the other globally; I tried wrapping only the offending lines in policy push/pops but CMake complains anyway because the policy wasn't set explicitly before the wrapping, i.e.

```
if (POLICY CMP0043)
	cmake_policy(PUSH)
	cmake_policy(SET CMP0043 OLD)
endif (POLICY CMP0043)
...
if (POLICY CMP0043)
	cmake_policy(POP)
endif (POLICY CMP0043)
```
does not work because it has to be set explicitly beforehand.

Fixes #506.