Fix ADD_DEFINITION in CMakeLists.txt for kFreeBSD

* CMakeLists.txt: Fix broken ADD_DEFINITION for kFreeBSD.
Fix CMakeLists.txt: do not override CMAKE_OSX_ARCHITECTURES

* CMakeLists.txt: Since latest OSX compiler (clang) provided by Xcode is
not accept "-arch ppc"; So if CMAKE_OSX_ARCHITECTURES is defined by
client, CMakeLists.txt should not force "ppc;i386;x86_64".
Update AUTHORS file