go: backport upstream fix for AVX

[kencu]

closes: https://trac.macports.org/ticket/60133

Description

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.13.6 17G11023
Xcode 10.1 10B61

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?

• checked your Portfile with port lint?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?

[macportsbot]

Notifying maintainers:
@ci42 for port go.

[macportsbot]

Travis Build #10551 Passed.

Lint results

--->  Verifying Portfile for go
--->  0 errors and 0 warnings found.

Port go success on xcode10.3. Log
Port go success on xcode9.4. Log
Port go success on xcode7.3. Log

[kencu]

this port is broken on many systems; this patch backports an existing upstream fix that is coming down the pipeline sooner or later. maintainer timeout.