Since some callers need the complain parameter but not the object
parameter, let's introduce and use an overload of cxx_constant_value
that omits the latter.
gcc/cp/ChangeLog:
* cp-tree.h (cxx_constant_value): Define two-parameter version
that omits the object parameter.
* decl.cc (build_explicit_specifier): Omit NULL_TREE object
argument to cxx_constant_value.
* except.cc (build_noexcept_spec): Likewise.
* pt.cc (expand_integer_pack): Likewise.
(fold_targs_r): Likewise.
* semantics.cc (finish_if_stmt_cond): Likewise.