env/openbsd-amd64: update build image script to OpenBSD 7.6

OpenBSD 7.6 has been released, meaning that the only two supported
versions are 7.5 and 7.6. Update the image build script for 7.6.

Additionally, bump the maxproc limit for the swarming user, which
will hopefully reduce the number of failures due to fork/exec
returning EAGAIN.

Updates golang/go#66474
Updates golang/go#69823

Change-Id: Ie2667de2defefbb6a56adca3dec92d7663c615e4
Reviewed-on: https://go-review.googlesource.com/c/build/+/618895
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

env/openbsd-amd64/README

@@ -3,18 +3,18 @@ OpenBSD builder, booting up to run the buildlet.
 
 make.bash should be run on a Linux box with expect and qemu.
 Debian packages: expect qemu-utils qemu-system-x86 growisofs genisoimage.
-    VERSION=7.2 ARCH=amd64 ./make.bash
+    VERSION=7.6 ARCH=amd64 ./make.bash
 
 After it completes, it creates a file openbsd-${VERSION}-${ARCH}-gce.tar.gz
 
 Then:
-    gsutil cp -a public-read openbsd-7.2-amd64-gce.tar.gz gs://go-builder-data/openbsd-amd64-72.tar.gz
+    gsutil cp -a public-read openbsd-7.6-amd64-gce.tar.gz gs://go-builder-data/openbsd-amd64-76.tar.gz
 Or just use the web UI at:
     https://console.developers.google.com/project/symbolic-datum-552/storage/browser/go-builder-data/
 
 Then:
-    gcloud compute --project symbolic-datum-552 images delete openbsd-amd64-72
-    gcloud compute --project symbolic-datum-552 images create openbsd-amd64-72 --source-uri gs://go-builder-data/openbsd-amd64-72.tar.gz
+    gcloud compute --project symbolic-datum-552 images delete openbsd-amd64-76
+    gcloud compute --project symbolic-datum-552 images create openbsd-amd64-76 --source-uri gs://go-builder-data/openbsd-amd64-76.tar.gz
 
 The VM needs to be run with the GCE metadata attribute "buildlet-binary-url" set to a URL
 of the OpenBSD buildlet (cross-compiled, typically).

env/openbsd-amd64/make.bash

@@ -7,7 +7,7 @@ set -e
 set -u
 
 # Update to the version listed on https://openbsd.org
-readonly VERSION="${VERSION:-7.2}"
+readonly VERSION="${VERSION:-7.6}"
 readonly RELNO="${VERSION/./}"
 readonly SNAPSHOT=false
 
@@ -63,18 +63,17 @@ moreres:\
   :vmemoryuse-cur=infinity: \
   :memoryuse-max=infinity: \
   :memoryuse-cur=infinity: \
-  :maxproc-max=1024: \
-  :maxproc-cur=1024: \
+  :maxproc-max=2048: \
+  :maxproc-cur=2048: \
   :openfiles-max=4096: \
   :openfiles-cur=4096: \
   :tc=default:
 EOLOGIN
 usermod -L moreres swarming
 syspatch
-# Run syspatch twice in case syspatch itself needs patching (this is the case with OpenBSD
-# 7.1: https://www.openbsd.org/errata71.html )
+# Run syspatch twice in case syspatch itself needs patching (this has been needed previously).
 syspatch
-pkg_add -iv ${PKG_ADD_OPTIONS} bash curl git python3 sudo--gettext
+pkg_add -iv ${PKG_ADD_OPTIONS} bash curl git python%3 sudo--gettext
 chown root:wheel /etc/sudoers
 halt -p
 EOF
@@ -124,7 +123,7 @@ swarming ALL=NOPASSWD:/sbin/shutdown -r now
 EOF
 chmod +x ${SITE}/install.site
 mkdir -p ${SITE}/usr/local/bin
-CGO_ENABLED=0 GOOS=openbsd GOARCH=${ARCH/i386/386} go1.21.0 build -o ${SITE}/usr/local/bin/bootstrapswarm golang.org/x/build/cmd/bootstrapswarm
+CGO_ENABLED=0 GOOS=openbsd GOARCH=${ARCH/i386/386} go build -o ${SITE}/usr/local/bin/bootstrapswarm golang.org/x/build/cmd/bootstrapswarm
 tar --mode a=rx,u=rwx --owner root:0 --group wheel:0 -C ${SITE} -zcf ${WORK}/site${RELNO}.tgz .
 
 # Autoinstall script.