Fix _wrapper_device_link artifact name conflict

[cloudhan]

Compile the newly added example with _wrapper_device_link with rdc cause artifact name conflict

rules_cuda/examples/rdc/BUILD.bazel

Lines 39 to 44 in 0503ead

	cuda_library(
	name = "b",
	srcs = ["b.cu"],
	hdrs = ["b.cuh"],
	rdc = True,
	)

The reason is because our compile always compile to <target_output_dir>/_objs:

cuda_library(name="b") --> artifact base name is `b` during `compile`

with `compile` for following srcs
"b.cu" ------------------> artifact `<target_output_dir>/_objs/b.rdc.o`
`fatbin.cu` ------rdc----> artifact `<target_output_dir>/_objs/b.rdc.o`

After this PR:
"b.cu" ------------------> artifact `<target_output_dir>/_objs/b.rdc.o`
`fatbin.cu` ------rdc----> artifact `<target_output_dir>/_objs/_dlink/b.rdc.o`

Note we reserve the _prefix keyword params for future change and keep it as (implicitly) internal.

[jsharpe]

Aren't you missing the change in this function to actually make use of this prefix?

[cloudhan]

Yes! Burried in another branch.