Revert "internal/poll: drop redundant ENOSYS and EXDEV error checks in CopyFileRange()"

Revert "internal/poll: drop redundant ENOSYS and EXDEV error checks in CopyFileRange()"

This reverts https://go.dev/cl/425881.

Reason for revert: broke make.bash on linux/amd64 with Linux 5.19.6.

	[...]
	Building Go toolchain2 using go_bootstrap and Go toolchain1.
	go install internal/unsafeheader: copying /tmp/go-build4206185186/b007/_pkg_.a to /home/mvdan/tip/pkg/linux_amd64/internal/unsafeheader.a: write /home/mvdan/tip/pkg/linux_amd64/internal/unsafeheader.a: copy_file_range: invalid cross-device link
	go install internal/goarch: copying /tmp/go-build4206185186/b006/_pkg_.a to /home/mvdan/tip/pkg/linux_amd64/internal/goarch.a: write /home/mvdan/tip/pkg/linux_amd64/internal/goarch.a: copy_file_range: invalid cross-device link
	[...]

Change-Id: I793856935d4315a870c2d31da46be00cc342b5f8
Reviewed-on: https://go-review.googlesource.com/c/go/+/428396
Reviewed-by: Wayne Zuo <wdvxdr@golangcn.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: hopehook <hopehook@golangcn.org>
Reviewed-by: Andy Pan <panjf2000@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>