CMake: add functions creating universal runtime libraries for several architectures on OS X and use them in ASan and UBSan build rules

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173011 91177308-0d34-0410-b5e6-96231b3b80d8
ASan: build runtime library with ASAN_FLEXIBLE_MAPPING_AND_OFFSET=1 as shadow mapping/offset are always emitted by the LLVM backend now

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@173013 91177308-0d34-0410-b5e6-96231b3b80d8