[clang-tidy] Build it even without static analyzer

Conditionally compile the parts of clang-tidy which depend on the static
analyzer.

Funnily enough, I made the patch to exclude this from the build in 2013,
and it was committed with the comment that the tool should not be fully
excluded, but only the parts of it which depend on the analyzer should
be excluded.

 http://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20130617/081797.html

This commit implements that idea.

Reviewed By: aaron.ballman

Tags: #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D52334

llvm-svn: 343528