[docs] Fix some finicky Sphinx warnings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190336 91177308-0d34-0410-b5e6-96231b3b80d8
[docs] Fix Sphinx toctree warning.

Last I heard LSan is getting close to prime-time, but for now keep
LeakSanitizer.rst hidden (especially since it contains so little
content).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190337 91177308-0d34-0410-b5e6-96231b3b80d8
[docs] End users should see just "Clang"

Half the internet has wildly incorrect ideas about what LLVM is (in
particular, many get the impression that LLVM is some magical
cross-platform runtime), so saying "LLVM" near "cross-compilation" in a
user-facing doc might provoke confusion.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190338 91177308-0d34-0410-b5e6-96231b3b80d8