minor cmake formatting style fix

git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@360142 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index d7d8e17..652d30e 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -36,7 +36,9 @@
 endif()
 
 if (LIBCXXABI_ENABLE_THREADS AND (UNIX OR FUCHSIA) AND NOT (APPLE OR CYGWIN))
-  list(APPEND LIBCXXABI_SOURCES cxa_thread_atexit.cpp)
+  list(APPEND LIBCXXABI_SOURCES
+    cxa_thread_atexit.cpp
+  )
 endif()
 
 set(LIBCXXABI_HEADERS