[clang][Bazel] Add missing dependency from symbol_graph to llvm:support.

This did not show up as build error because the build also works if the
dependency is transitively available. But there should be a direct
dependency anyway.

utils/bazel/llvm-project-overlay/clang/BUILD.bazel

@@ -1298,6 +1298,7 @@ cc_library(
         ":basic",
         ":frontend",
         ":index",
+        "//llvm:Support",
     ],
 )