[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: fafd45c01f3a49a40b09a31e9ea82efc87f3ab35
3 files changed