[OpenMP] Fix offload packager not writing to temps correctly

The offloading packager doesn't have a normal offloading kind. This
would result in its output being sent to the executable name when in
save-temps mode. This would then get overwritten by the actual output.
This patch adds specific checks to make sure that it gets the correct
name.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D127673