Some libc functions are suffixed with "$INODE64" on macOS.
Unfortunately, the iOS simulator doesn't have the suffixes, so we can't
use GOARCH to distinguish the two platform.

Add linker support for adding the suffix, using the macho platform
to determine whether it is needed.

While here, add the correct suffix for fdopendir on 386. It's
"$INODE64$UNIX2003", believe it or not. Without the suffix,

GOARCH=386 go test -short syscall

crashes on my Mojave machine.

Fixes #31447

Change-Id: I9bd3de40ece7df62f744bc24cd00909e56b00b78
Reviewed-on: https://go-review.googlesource.com/c/go/+/174199
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>