net-p2p/amule: fix build on 32-bit platforms properly

The port asks for libatomic on 32 bit platforms. That's a gcc thing.
We don't compile with gcc, so libatomic is not needed in any case.
Patch out the check for libatomic to fix the build on all 32-bit
platforms.

Approved by: portmgr (build fix blanket)
MFH: 2026Q3