Use correct CMake variable for the libname

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@250329 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index a3b50a7..d02b8c5 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -138,7 +138,7 @@
 if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
   # Get the name of the ABI library and handle the case where CXXABI_LIBNAME
   # is a target name and not a library. Ex cxxabi_shared.
-  set(SCRIPT_ABI_LIBNAME "${CXXABI_LIBNAME}")
+  set(SCRIPT_ABI_LIBNAME "${LIBCXX_CXX_ABI_LIBRARY}")
   if (SCRIPT_ABI_LIBNAME STREQUAL "cxxabi_shared")
     set("${SCRIPT_ABI_LIBNAME}" "c++abi")
   endif()