Update test checks for Clang-Doc

[ilovepi]

UTC is a valuable utility for LLVM developers to update tests due to mechanical changes in codegen that affect a lot of tests.

Like those LLVM passes, changes to Clang-Doc's templates or core data structures often cause a lot of churn in our test output.

It would be best if we had a utility, like UTC that could update our test outputs in a maintainable way.

This could be done either by extending some of the functionality in the UTC scripts, or by writing our own version that reuses the UTC modules.

[ilovepi]

CC: @evelez7 @petrhosek

[evelez7]

From poking around somewhat briefly in the UTC files, it looks like it expects an out stream to get the test output. Do you think it'd be better to extend clang-doc to output to a stream or for UTC to parse individual files? Also do you think this would live in clang-tools-extra or llvm? I think we'd need a lot of the functionality that lives in llvm.