testsuite, c++: Account for missing stong symbol aliases.

Darwin does not have strong symbol aliases and therefore must emit complete
constructors (which might, or might not call others).  Several tests assume
that a base constructor is emitted (which is fine for targets with strong
symbol aliases that emit the complete constructor symbol as an alias to the
base etc.).

Handle the two cases with separate matches.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/clone-4_b.C: Account for missing strong symbol
	aliases.
	* g++.dg/template/explicit-instantiation8.C: Likewise.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit bef4f0f92a9ffe624ab3f7fbf565a8587926c4d4)