swift234

CMake: Add COMPILE_FLAGS support for add_swift_library.

COMPILE_FLAGS is currently used for two purposes:
  - For any target library, add the appropriate Swift optimization flags. This eliminates the add_swift_optimization_flags boilerplate and makes these flags work for all library variants
  - For the runtime, pass the appropriate define down when SWIFT_RUNTIME_CLOBBER_FREED_OBJECTS is set, so that all library variants get this setting.

Swift SVN r19444