From https://github.com/bitcoin/bitcoin/blob/master/doc/fuzzing.md#macos-hints-for-libfuzzer:
brew install llvm
...
$ cmake --preset=libfuzzer -DCMAKE_C_COMPILER="$(brew --prefix llvm)/bin/clang" -DCMAKE_CXX_COMPILER="$(brew --prefix llvm)/bin/clang++" -DAPPEND_LDFLAGS=-Wl,-no_warn_duplicate_libraries
Originally posted by @sipa in #31111 (comment)