Improve our handling of C++ [class.copy]p3, which specifies that a

Improve our handling of C++ [class.copy]p3, which specifies that a
constructor template will not be used to copy a class object to a
value of its own type. We were eliminating all constructor templates
whose specializations look like a copy constructor, which eliminated
important candidates. Fixes PR8182.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@118418 91177308-0d34-0410-b5e6-96231b3b80d8