Generate nuw GEPs for struct member accesses, as inbounds + non-negative
implies nuw.
Regression tests are updated using update scripts where possible, and by
find + replace where not.
If use_device_ptr/use_device_addr clauses are used on target data
directive and no device was specified during the compilation, only host
part should be emitted. But it still required to emit captured decls for
partially mapped data fields.
Differential Revision: https://reviews.llvm.org/D144993