testsuite, Objective-C: Fix duplicate libobjc cases.

testsuite, Objective-C: Fix duplicate libobjc cases.

Two of the encode testcases include '-lobjc' as their dg-options.
Since the library is already appended as part of the generic testsuite
handling,  this means that two instances appear on the link line leading
to spurious warnings from Darwin's new linker.

gcc/testsuite/ChangeLog:

	* obj-c++.dg/encode-10.mm: Remove unneeded '-lobjc' option addition.
	* obj-c++.dg/encode-9.mm: Likewise.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
(cherry picked from commit 30d9e81c19d69e15b2e9c53e4377879cbf9b0b84)