[Libomptarget][Obvious] Fix incorrect if-else in CMake for destination

Summary:
This was added in a previous patch to update how we export the static
library used for OpenMP offloading. By mistake this if-else was using
the output incorrectly.

Fixes https://github.com/llvm/llvm-project/issues/74079

GitOrigin-RevId: 52fe16a47e2e7a09e10830fee489eeeeef7fd130
2 files changed