c++/modules: Propagate BINDING_VECTOR_*_DUPS_P on realloc [PR99242]

c++/modules: Propagate BINDING_VECTOR_*_DUPS_P on realloc [PR99242]

When importing modules, when a binding vector for a name runs out of
slots it gets reallocated with a larger size, and existing bindings are
copied across.  However, the flags to indicate whether deduping needs to
occur did not: this causes ICEs, as it allows a duplicate binding to be
added which then violates assumptions later on.

	PR c++/99242

gcc/cp/ChangeLog:

	* name-lookup.cc (append_imported_binding_slot): Propagate dups
	flags.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr99242_a.H: New test.
	* g++.dg/modules/pr99242_b.H: New test.
	* g++.dg/modules/pr99242_c.H: New test.
	* g++.dg/modules/pr99242_d.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>