cmd/link: mark ELF PLT sections executable
cmd/link: mark ELF PLT sections executable

Change-Id: Ie0316a06c30485f783c2175590d7e9fc4fa3e0cd
Reviewed-on: https://go-review.googlesource.com/c/go/+/253021
Run-TryBot: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>

golang/go,nawawi/go,nawawi/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,golang/go,nawawi/go,golang/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,nawawi/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,CAFxX/go,nawawi/go