Change go/build.readDir to use os.ReadDir instead of ioutil.ReadDir.
This addresses a TODO and improves performance on Darwin and Linux.
Darwin: Apple M1
name old time/op new time/op delta
ImportVendor-10 39.8µs ± 1% 37.0µs ± 1% -6.91% (p=0.000 n=10+10)
Linux: Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz
name old time/op new time/op delta
ImportVendor-16 22.9µs ±11% 21.2µs ± 5% -7.47% (p=0.001 n=10+9)
Updates #45557
Change-Id: Ib1bd2e66210e714e499a035847d6261b61b7e2c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/392074
Run-TryBot: Ian Lance Taylor <iant@google.com> Reviewed-by: Daniel Martí <mvdan@mvdan.cc> Reviewed-by: Ian Lance Taylor <iant@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>