When we are performing copy initialization of a class type via its

When we are performing copy initialization of a class type via its
copy constructor, suppress user-defined conversions on the
argument. Otherwise, we can end up in a recursion loop where the
bind the argument of the copy constructor to another copy constructor call,
whose argument is then a copy constructor call...

Found by Boost.Regex which, alas, still isn't building.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102269 91177308-0d34-0410-b5e6-96231b3b80d8