[libomptarget][cuda] Gracefully handle missing cuda library

[libomptarget][cuda] Gracefully handle missing cuda library

If using dynamic cuda, and it failed to load, it is not safe to call
cuGetErrorString.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D95412

GitOrigin-RevId: 7baff00eeedb0d9bac5e7cd0c5e4189a6cc6101d
3 files changed