env/freebsd-amd64: update FreeBSD 12.0 to a -RELEASE image

Install GDB from the ports collection, the in-tree was removed from the base system
in FreeBSD 12.0, and the older releases have an unsupported (6.1.1 or older version).

Updates golang/go#25289

Change-Id: I8899a2a70c0b9ee9171621206431ca24a7e97704
Reviewed-on: https://go-review.googlesource.com/c/155977
Reviewed-by: Brad Fitzpatrick <[email protected]>

Author: paulzhol

dashboard/builders.go

@@ -204,8 +204,8 @@ var Hosts = map[string]*HostConfig{
 		SSHUsername:        "gopher",
 	},
 	"host-freebsd-12_0": &HostConfig{
-		VMImage:            "freebsd-amd64-120a8",
-		Notes:              "FreeBSD 12.0alpha8; GCE VM is built from script in build/env/freebsd-amd64",
+		VMImage:            "freebsd-amd64-120-v1",
+		Notes:              "FreeBSD 12.0; GCE VM is built from script in build/env/freebsd-amd64",
 		machineType:        "n1-highcpu-4",
 		buildletURLTmpl:    "https://storage.googleapis.com/$BUCKET/buildlet.freebsd-amd64",
 		goBootstrapURLTmpl: "https://storage.googleapis.com/$BUCKET/go1.4-freebsd-amd64.tar.gz",

env/freebsd-amd64/make.bash

@@ -56,10 +56,9 @@ case $1 in
   readonly SHA256=d8638aecbb13bdc891e17187f3932fe477f5655846bdaad8fecd60614de9312c
 ;;
 12.0)
-  readonly VERSION=12.0-ALPHA8
-  readonly IS_SNAPSHOT=1
+  readonly VERSION=12.0-RELEASE
   readonly VERSION_TRAILER=
-  readonly SHA256=11c69e6511e754a81b0b7c7c35b5fb4eee4c24a9231f77d494cb2e4ac0958576
+  readonly SHA256=9eb70a552f5395819904ed452a02e5805743459dbb1912ebafe4c9ae5de5eb53
 ;;
 *)
   echo "Usage: $0 <version>"
@@ -180,7 +179,7 @@ if {$::env(DOWNLOAD_UPDATES)} {
 
 expect -re $prompt
 sleep 1
-send "pkg install bash curl git\n"
+send "pkg install bash curl git gdb\n"
 expect "Do you want to fetch and install it now"
 sleep 1
 send "y\n"