Implement redeclaration checking and hiding semantics for using declarations.  There
are a couple of O(n^2) operations in this, some analogous to the usual O(n^2)
redeclaration problem and some not.  In particular, retroactively removing
shadow declarations when they're hidden by later decls is pretty unfortunate.
I'm not yet convinced it's worse than the alternative, though.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@91045 91177308-0d34-0410-b5e6-96231b3b80d8
14 files changed