PR18246: When performing template argument deduction to decide which template
is specialized by an explicit specialization, start from the first declaration
in case we've got a member of a class template (redeclarations might not number
the template parameters the same way).

Our recover here is still far from ideal.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@197305 91177308-0d34-0410-b5e6-96231b3b80d8