[OpenMP][VE plugin] Fixing failure to build VE plugin with consolidated error...

[OpenMP][VE plugin] Fixing failure to build VE plugin with consolidated error handling in libomptarget

The libomptarget VE plugin [[
http://lab.llvm.org:8014/builders/clang-ve-ninja/builds/8937/steps/build-unified-tree/logs/stdio
| fails zu build ]] after ae95ceeb .

Differential Revision: https://reviews.llvm.org/D88476