archive/tar: fix sparse files support on Darwin
archive/tar: fix sparse files support on Darwin

Apple defined the SEEK_HOLE/SEEK_DATA constants in unistd.h
with swapped values, compared to all other UNIX systems.

Fixes #21970

Change-Id: I84a33e0741f0f33a2e04898e96b788b87aa9890f
Reviewed-on: https://go-review.googlesource.com/65570
Reviewed-by: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>
Run-TryBot: Joe Tsai <7277d7402195d5c2006c89f45718cf82bb3e527f@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

akutz/go,nawawi/go,golang/go,josharian/go,nawawi/go,polyverse-security/go,polyverse-security/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,josharian/go,polyverse-security/go,josharian/go,akutz/go,Cofyc/go,codestation/go,golang/go,CAFxX/go,nawawi/go,christopher-henderson/Go,polyverse-security/go,codestation/go,nawawi/go,Cofyc/go,polyverse-security/go,CAFxX/go,cloudflare/go,polyverse-security/go,nawawi/go,CAFxX/go,codestation/go,CAFxX/go,codestation/go,cloudflare/go,golang/go,cloudflare/go,codestation/go,akutz/go,cloudflare/go,akutz/go,Cofyc/go,akutz/go,josharian/go,CAFxX/go,Cofyc/go,codestation/go,Cofyc/go,akutz/go,Cofyc/go,polyverse-security/go,Cofyc/go,cloudflare/go,cloudflare/go,golang/go,josharian/go,josharian/go,josharian/go,codestation/go,cloudflare/go,codestation/go,golang/go,nawawi/go,cloudflare/go,polyverse-security/go,akutz/go,golang/go,golang/go,CAFxX/go,josharian/go,nawawi/go,Cofyc/go,akutz/go