Include clang-check as part of the clang installation.

This also tidies up a couple of other tools we were (partially) installing:
* c-index-test was being installed but shouldn't be (it's just a clang-dev tool)
* diagtool was being installed in cmake but not make (& shouldn't be installed in either)

Review by Manuel Klimek, Doug Gregor, and Chandler Carruth.

llvm-svn: 161073