[c-index-test] CMake: add missing reference to clangSerialization library.

llvm-svn: 293466
diff --git a/clang/tools/c-index-test/CMakeLists.txt b/clang/tools/c-index-test/CMakeLists.txt
index b845af0..7244e2c 100644
--- a/clang/tools/c-index-test/CMakeLists.txt
+++ b/clang/tools/c-index-test/CMakeLists.txt
@@ -27,6 +27,7 @@
     clangCodeGen
     clangFrontend
     clangIndex
+    clangSerialization
   )
 endif()