Do not list LLVM_LIBS in the target_link_libraries.

When using various prepackaged versions of LLVM 6.0, I was seeing fatal
errors like this when I ran `clang_delta`:

```
$ clang_delta --help
: CommandLine Error: Option 'disable-symbolication' registered more than once!
LLVM ERROR: inconsistency in registered CommandLine options
```

In some way that I do not understand, removing `LLVM_LIBS` from the call
to `target_link_libraries` seems to avoid this problem.  The LLVM
libraries end up in the link line anyway, also for reasons that I do not
understand.

Did I mention that I do not understand the current LLVM CMake magic?

clang_delta/CMakeLists.txt

@@ -242,7 +242,11 @@ add_executable(clang_delta
   git_version.h
 )
 
-target_link_libraries(clang_delta ${CLANG_LIBS} ${LLVM_LIBS})
+# ENE, LLVM 6.0: LLVM_LIBS end up in the link command line anyway.  I'm not
+# quite sure why!  But if you list LLVM_LIBS here, the `clang_delta' binary
+# can end up with dynamic link errors when it runs (multiply defined symbols).
+#
+target_link_libraries(clang_delta ${CLANG_LIBS})
 
 # Custom target for running clang_delta tests
 #