[Doc parsing]: This patch adds <Declaration> tag to

XML comment for declarations which pretty-prints
declaration. I had to XFAIL one test annotate-comments.cpp.
This test is currently unmaintainable as written.
Dmitri G., can you see what we can do about this test.
We should change this test such that adding a new tag does not wreck
havoc to the test.

llvm-svn: 166130