cmd/link: split large text sections on Darwin/ARM64 when external linking

The Darwin linker does not like text sections that are larger
than the jump limit (even if we already inserted trampolines).
Split the text section to multiple smaller sections.

Now external linking very large binaries works on Darwin/ARM64.

Updates #40492.

Change-Id: I584f1ec673170c5e4d2dc1e00c701964d6f14333
Reviewed-on: https://go-review.googlesource.com/c/go/+/316050


Trust: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>