Import CL 174738 and CL 164862 from std lib version. This should fix
test failures of issue31540.go on gccgo versions < 7, e.g. on
solaris-amd64-smartosbuildlet
Change-Id: I0a41ca9fe2b248d301fbdf14c9bac3aa3e7b091c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/180897
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>