Update Go to 1.10. Via wip.

Full release notes at https://golang.org/doc/go1.10.

The latest Go release, version 1.10, arrives six months after Go 1.9. Most of
its changes are in the implementation of the toolchain, runtime, and libraries.
As always, the release maintains the Go 1 promise of compatibility. We expect
almost all Go programs to continue to compile and run as before.

This release improves caching of built packages, adds caching of successful
test results, runs vet automatically during tests, and permits passing string
values directly between Go and C using cgo. A new compiler option whitelist may
cause unexpected invalid flag errors in code that built successfully with older
releases.

As announced in the Go 1.9 release notes, Go 1.10 now requires FreeBSD 10.3 or
later; support for FreeBSD 9.3 has been removed.

Go now runs on NetBSD again but requires the unreleased NetBSD 8. Only GOARCH
amd64 and 386 have been fixed. The arm port is still broken.

On 32-bit MIPS systems, the new environment variable settings GOMIPS=hardfloat
(the default) and GOMIPS=softfloat select whether to use hardware instructions
or software emulation for floating-point computations.

Go 1.10 is the last release that will run on OpenBSD 6.0. Go 1.11 will require
OpenBSD 6.2.

Go 1.10 is the last release that will run on OS X 10.8 Mountain Lion or OS X
10.9 Mavericks. Go 1.11 will require OS X 10.10 Yosemite or later.

Go 1.10 is the last release that will run on Windows XP or Windows Vista. Go
1.11 will require Windows 7 or later.

(bsiegert)