Keep track of whether a member function instantiated from a member

Keep track of whether a member function instantiated from a member
function of a class template was implicitly instantiated, explicitly
instantiated (declaration or definition), or explicitly
specialized. The same MemberSpecializationInfo structure will be used
for static data members and member classes as well.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@83509 91177308-0d34-0410-b5e6-96231b3b80d8