Restartable syscalls on BSDs

[nbuwe]

When I ported Self VM to NetBSD and FreeBSD one kludge I had to not use SA_RESTART like linux does. I didn't have time to figure out what was wrong, I might have messed up elsewhere in the Self code (cf. setAsyncIfFail and friends).

self/vm/src/unix/os/sig_unix.hh

Lines 47 to 52 in fcbb0d4

	# elif TARGET_OS_VERSION == NETBSD_VERSION \
	|| TARGET_OS_VERSION == FREEBSD_VERSION
	// This needs to play along with setNotifyEvents and setAsync - and
	// with SA_RESTART it doesn't (cf. unix.self). I'm not quite sure
	// why yet. For now just commit what is known to work.
	static int install_flags() { return SA_ONSTACK | SA_SIGINFO; }

This also most likely has implications for InterruptedContext::in_system_trap b/c the pc will not be pointing to the trap instruction, but past it.

This is a reminder that this issue needs further investigation.

[russellallen]

Note for myself: I've confirmed this happens.
I thought it was causing socket issues, but that was e67fe3f