doc: GOFLAGS environment variable not in 1.11 release notes

[andybons]

Commit message introducing it:

    cmd/go: add $GOFLAGS environment variable
    
    People sometimes want to turn on a particular go command flag by default.
    In Go 1.11 we have at least two different cases where users may need this.
    
    1. Linking can be noticeably slower on underpowered systems
    due to DWARF, and users may want to set -ldflags=-w by default.
    
    2. For modules, some users or CI systems will want vendoring always,
    so they want -getmode=vendor (soon to be -mod=vendor) by default.
    
    This CL generalizes the problem to “set default flags for the go command.”
    
    $GOFLAGS can be a space-separated list of flag settings, but each
    space-separated entry in the list must be a standalone flag.
    That is, you must do 'GOFLAGS=-ldflags=-w' not 'GOFLAGS=-ldflags -w'.
    The latter would mean to pass -w to go commands that understand it
    (if any do; if not, it's an error to mention it).
    
    For #26074.
    For #26318.
    Fixes #26585.
    
    Change-Id: I428f79c1fbfb9e41e54d199c68746405aed2319c
    Reviewed-on: https://go-review.googlesource.com/126656
    Run-TryBot: Russ Cox <rsc@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: Rob Pike <r@golang.org>

[n]

@andybons Can the documentation also clarify how to assign a space delimited argument list?
GOFLAGS='-ldflags="-w -s"' go build
go: parsing $GOFLAGS: unknown flag -s"

[thepudds]

Setting aside the release notes for a moment, there is basic documentation here:

https://tip.golang.org/cmd/go/#hdr-Environment_variables

[agnivade]

@n -

A space-separated list of -flag=value settings

So - GOFLAGS="-ldflags=-w -ldflags=-s"

[FiloSottile]

@gopherbot please file this for backport against 1.11, so the release notes will get updated.

@andybons please make a cherry-pick CL once your change is merged in master.

[gopherbot]

Backport issue(s) opened: #27387 (for 1.11).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.