OpenMP: Fix use_device_{addr,ptr} with in-data-sharing arg

OpenMP: Fix use_device_{addr,ptr} with in-data-sharing arg

For array-descriptor vars, the descriptor is assigned to a temporary. However,
this failed when the clause's argument was in turn in a data-sharing clause
as the outer context's VALUE_EXPR wasn't used.

gcc/ChangeLog:

	* omp-low.cc (lower_omp_target): Fix use_device_{addr,ptr} with list
	item that is in an outer data-sharing clause.

libgomp/ChangeLog:

	* testsuite/libgomp.fortran/use_device_addr-5.f90: New test.