[CMake] Add more runtime configurations.

Summary:
- `project` is required when `runtime/CMakeList.txt` is the top-level `CMakeList.txt` file. This will establish version and policy settings.

- `-D_FILE_OFFSET_BITS=64` should never be set for Android runtimes.

Reviewers: srhines, pirama, beanz

Subscribers: llvm-commits, srhines, mgorny

Differential Revision: https://reviews.llvm.org/D35648

llvm-svn: 312302