[Rewrite] Try to fix buildbot link fail left by r365263

http://lab.llvm.org:8011/builders/clang-ppc64le-linux-multistage/builds/10272

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@365264 91177308-0d34-0410-b5e6-96231b3b80d8

unittests/Rewrite/CMakeLists.txt

@@ -10,5 +10,6 @@ clang_target_link_libraries(RewriteTests
   PRIVATE
   clangFrontend
   clangRewrite
+  clangSerialization
   clangTooling
   )