Add a makefile for clang-query. Patch by Alex Horn!

While at it, have cmake build and test the tool if libedit is not installed,
as this dependency is now optional.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@201599 91177308-0d34-0410-b5e6-96231b3b80d8