[CMake] Don't require libcxxabi on darwin

Just libcxx should suffice.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@349546 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/CMakeLists.txt b/CMakeLists.txt
index f16cdf3..48751ec 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -159,7 +159,6 @@
     list(APPEND LLDB_TEST_DEPS clang)
     if(APPLE)
       list(APPEND LLDB_TEST_DEPS cxx)
-      list(APPEND LLDB_TEST_DEPS cxxabi)
     endif()
   endif()