Revert "[CMake][libcxx] Check that we have libcxxabi before using it"

This reverts commit 8c91834411b322ab360eb1f193f489327e719652.

llvm-svn: 291726

libcxx/CMakeLists.txt

@@ -119,8 +119,7 @@ if (LIBCXX_CXX_ABI STREQUAL "default")
           ${LLVM_MAIN_SRC_DIR}/runtimes/libcxxabi/include
     NO_DEFAULT_PATH
   )
-  if ((NOT LIBCXX_STANDALONE_BUILD OR HAVE_LIBCXXABI) AND
-      IS_DIRECTORY "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
+  if (IS_DIRECTORY "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
     set(LIBCXX_CXX_ABI_LIBNAME "libcxxabi")
     set(LIBCXX_CXX_ABI_INCLUDE_PATHS "${LIBCXX_LIBCXXABI_INCLUDES_INTERNAL}")
     set(LIBCXX_CXX_ABI_INTREE 1)