test: fix nosplit.go, fixedbugs/issue11656.go and skip two tests for mips64{,le}

Skip fixedbugs/issue10607.go because external linking is not supported
yet.

Skip nilptr3.go because of issue #9058 (same as ppc64).

Change-Id: Ib3dfbd9a03ee4052871cf57c74b3cc5e745e1f80
Reviewed-on: https://go-review.googlesource.com/14461


Reviewed-by: Minux Ma <minux@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>