cmd/compile/internal/base: replace io/ioutil with os package
Change-Id: Ide7618b65fcff7947809051d51b993d330e35717
GitHub-Last-Rev:
298853a82006655fe4f226cc5bea3bc21613b832
GitHub-Pull-Request: golang/go#55914
Reviewed-on: https://go-review.googlesource.com/c/go/+/435537
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>