runtime: Support Solaris AMD64 in lfstack.
The address space layout is similar on SPARC64 and AMD64 when
running Solaris.

R=gofrontend-dev, iant
CC=gofrontend-dev
https://codereview.appspot.com/7307127

Committer: Ian Lance Taylor <iant@golang.org>
syscall: Solaris fixes for passing file descriptor.

From Rainer Orth.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56171

R=iant
CC=gofrontend-dev
https://codereview.appspot.com/7398043