CMake does not detect libatomic.so

[mjklemm]

Describe the bug The build system does not correctly detect the link-line flags for libatomic.so, which is needed for a compilation with GCC.

To Reproduce Please provide steps to reproduce the behavior:

1. Configure LOMP using CMake.
2. Compile LOMP.
3. Do ldd src/libomp.so
4. The libatomic.so library is missing from the library dependencies (also the GCC linker shows errors to atomics)

Expected behavior Correctly link libatomic.so.

Screenshots n/a

Desktop (please complete the following information):

• OS: Linux
• Target architecture: x86_86, likely all
• LOMP Version: 0.2 and latest main