[OpenMP][Tests][NFC] Mark unsupported libomp tests for GCC

This patch properly marks the support level for libomp test when testing with
GCC.

Some new OpenMP features were only introduced with GCC 11.
Tests using the target construct are incompatibe with GCC.

Tests pass now with GCC 10, 11, 12

GitOrigin-RevId: fe7f620ed6e30015267d131bb753fd408bb3dd8c
7 files changed