[dev.power64] liblink: fix $large(SP) for floating point load/store

Fixes test/cmplxdivide.

LGTM=minux
R=minux
CC=golang-codereviews
https://codereview.appspot.com/128190045
[dev.power64] reflect: now we find one big endian machine

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/124350043

Committer: Russ Cox <rsc@golang.org>
[dev.power64] runtime: fix time.now

Was reading a uint64 field with a MOVW, which has endian issues.

LGTM=rsc
R=rsc, iant
CC=golang-codereviews
https://codereview.appspot.com/122550043

Committer: Russ Cox <rsc@golang.org>