Test for weak undefined symbols in linknamespace.pl.

This patch makes linknamespace.pl require weak undefined symbols to be
within the standard namespace.  (It remains the case that
linknamespace.pl does not look for definitions of such symbols or
require symbols used in those definitions to be within the standard
namespace.)

Tested for x86_64 and x86.

	* conform/linknamespace.pl: Require weak undefined symbols to be
	in the standard namespace.
	(%strong_syms): Rename to %seen_syms.
	(%strong_seen): Rename to %seen_where.