cmd/objdump: disable unsupported tests on riscv64
cmd/objdump: disable unsupported tests on riscv64

Updates #27532, #36738 and #36739.

Change-Id: If10031c6fd2c8ec2aa8c37f7edb148d8f26f8697
Reviewed-on: https://go-review.googlesource.com/c/go/+/216258
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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