[release-branch.go1.11] cmd/go: add GOMIPS value to build id for mipsle

Strip a trailing "le" from the GOARCH value when calculating the GOxxx
environment variable that affects it.

Updates #27260
Fixes #27420

Change-Id: I081f30d5dc19281901551823f4f56be028b5f71a
Reviewed-on: https://go-review.googlesource.com/131379


Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
(cherry picked from commit 61318d7f)
Reviewed-on: https://go-review.googlesource.com/138176


Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>