PR19091: Track whether we're demangling a function template specialization to
determine whether we get a mangling for a return type, rather than trying to
figure it out based on whether the mangled name ended with a '>'.


git-svn-id: https://llvm.org/svn/llvm-project/libcxxabi/trunk@208611 91177308-0d34-0410-b5e6-96231b3b80d8