Implement dependent alignment attribute support. This is a bit gross given the

current attribute system, but it is enough to handle class templates which
specify parts of their alignment in terms of their template parameters.

This also replaces the attributes test in SemaTemplate with one that actually
tests working attributes instead of broken ones. I plan to add more tests here
for non-dependent attributes in a subsequent patch.

Thanks to John for walking me through some of this. =D

llvm-svn: 106818