[PATCH] Propagate cv qualifications in variant_alternative

[Jonathan Wakely]

On 21/11/16 22:46 -0800, Tim Shen wrote:
>    	PR libstdc++/78441
>    	* include/std/variant: Propagate cv qualifications to types returned
>    	by variant_alternative.
>    	* testsuite/20_util/variant/compile.cc: Tests.

OK for trunk, thanks.