cmd/compile/internal/importer,go/internal/gcimporter: use the 'go' command from build.Default.GOROOT in lookupGorootExport
Also set GOROOT explicitly in case it is set to something else in the
caller's environment.
Updates #59598.
Fixes #59637.
Change-Id: I5599ed1183b23187fc3b976786f3c320d42ef4f3
Reviewed-on: https://go-review.googlesource.com/c/go/+/484756
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
(cherry picked from commit
750e91152bbd1cb2869660ddb80f2b3adcfd1f9b)
Reviewed-on: https://go-review.googlesource.com/c/go/+/484758
Auto-Submit: Dmitri Shuralyov <dmitshur@google.com>