Make libfuzzer to work on macOS

Summary:
This makes it possible to build with libfuzzer on macOS (PR18008), fix
the issue that this PR introduced for other platforms (PR19366) and add
the corresponding documentation (PR17942).

This is a backport of core PR17942, PR18008 and PR19366.

Test Plan:
On macOS, read the documentation and follow the instructions.
I only ran the instructions for libfuzzer.

ninja bitcoin-fuzzers
./test/fuzz/test_runner.py <path_to_corpus>

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D8956