Recommendations for fuzzing tools?

Hi! I've been looking into using fuzzing to test some of the things I'm working on.

It looks like libFuzzer is included in the Swift developer snapshot, but not in the official release, and it doesn't look like the version of the compiler used by Xcode has the libFuzzer code available.

The compiler does understand the complier flags for turning on fuzzing, but ends up with unresolved symbols--and the library's not in the tree that I've beenn able to find...

___sanitizer_cov_8bit_counters_init", referenced from: _sancov.module_ctor in main.o ___sanitizer_cov_pcs_init", referenced from: _sancov.module_ctor in main.o

Has anyone been working with fuzzing tools + XCTest? Fuzzing Objective-C code? Fuzzing Swift code?

Any recommendations for tools that you've used which perform well? Preferably ones that are relatively mature, but given the apparent dearth of options I might need to waive that part...