Enable fuzzing support on macOS by configuring the build system to use Homebrew LLVM toolchain and handle macOS-specific linking requirements.
The `make check-fuzz` command was failing on macOS because:
- System clang lacks fuzzer runtime library support
- Linking issues with fuzzer targets
- Test script attempts to execute debug symbol files
This PR adds macOS-specific configuration to:
- Use Homebrew LLVM toolchain for fuzzer support
- Explicitly link fuzzer libraries
- Exclude `.dSYM` directories from test discovery
All 76 fuzzer targets now build and pass on macOS.
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