Introduce a second queue of "local" pending implicit instantiation,

which are instantiations of the member functions of local
classes. These implicit instantiations have to occur at the same time
as---and in the same local instantiation scope as---the enclosing
function, since the member functions of the local class can refer to
locals within the enclosing function. This should really, really fix PR5764.

llvm-svn: 93666