c++: unifying identical tmpls from current inst [PR108347]
Here more_specialized_partial_spec wrongly considers the two partial
specializations to be unordered ultimately because unify for identical
parm=arg=A<T>::C returns failure due to C being dependent.
This patch fixes this by relaxing unify's early-exit identity test to
also accept dependent decls; we can't deduce anything further from them
anyway. In passing this patch removes the CONST_DECL case of unify:
we should never see the CONST_DECL version of a template parameter here,
and for other CONST_DECLs (such as enumerators) it seems we can rely on
them to already have been folded to their DECL_INITIAL.
PR c++/108347
gcc/cp/ChangeLog:
* pt.cc (unify): Return unify_success for identical dependent
DECL_P 'arg' and 'parm'.
<case CONST_DECL>: Remove handling.