I think I've done about as much as I can reasonably do for this.
Will open new issues if necessary.
Remaining regtest faulures are due to:
many many many Darwin leaks
debuginfo differences
unsupported x86 opcodes
libpthread race in stack teardown (?) - fixed in macOS 10.14
Darwin has different output of v.info monitor request
510864 Add SSE4.1 PMAXSD and PMINSD instructions support for 32-bit x86
511329 Darwin and FreeBSD: Move setting of carry flag out of
ML_(do_syscall_for_client_WRK)
+511461 Darwin 17 (MacOS X 10.13) memcheck issues
511713 Refactor syscall argument handling
511717 gdbserver (valgrind_read_memory) the 'impossible' happened:
Killed by fatal signal (SIGSEGV)