internal/releasetargets: update linux-{386,amd64} builders to buster

We've updated the Linux builders used during Go releases from
Debian 8 "Jessie" to Debian 9 "Stretch" in time for Go 1.16,
since Jessie support had already ended on June 30, 2020 and
wasn't suitable for the lifetime of Go 1.16.

We're in a similar position now, where Debian 9 "Stretch" LTS
support is ending on June 30, 2022, before Go 1.19's anticipated
release date. Update the selected builder to Debian 10 "Buster",
whose LTS support keeps going until June 2024 and should cover
the expected lifespan of Go 1.19 better.

This is easy to do thanks to the builder already being added
as of CL 267937.

For golang/go#40561.
Updates golang/go#42410.

Change-Id: I06b43e1cdd66996852ed19a1cc928eff29d09c86
Reviewed-on: https://go-review.googlesource.com/c/build/+/410094
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

internal/releasetargets/releases.txt

@@ -76,3 +76,42 @@ windows-arm64   windows    arm64      windows-arm64-11
 
 
 
+Targets for release 1.19
+================================================================================
+darwin-amd64    darwin     amd64      darwin-amd64-12_0
+	Race enabled
+	Extra env: ["CGO_CFLAGS=-mmacosx-version-min=10.13"]
+
+darwin-arm64    darwin     arm64      darwin-arm64-12
+	Race enabled
+
+freebsd-386     freebsd    386        freebsd-386-12_3
+
+freebsd-amd64   freebsd    amd64      freebsd-amd64-12_3
+	Race enabled
+
+linux-386       linux      386        linux-386-buster
+	Long tests on linux-386-longtest
+
+linux-amd64     linux      amd64      linux-amd64-buster
+	Race enabled, Long tests on linux-amd64-longtest
+
+linux-arm64     linux      arm64      linux-arm64-aws
+
+linux-armv6l    linux      arm        linux-arm-aws
+
+linux-ppc64le   linux      ppc64le    linux-ppc64le-buildlet
+	Build only
+
+linux-s390x     linux      s390x      linux-s390x-crosscompile
+	Build only
+
+windows-386     windows    386        windows-386-2008
+
+windows-amd64   windows    amd64      windows-amd64-2008
+	Race enabled, Long tests on windows-amd64-longtest
+
+windows-arm64   windows    arm64      windows-arm64-11
+
+
+

internal/releasetargets/releasetargets.go

@@ -108,6 +108,17 @@ var allReleases = map[int]ReleaseTargets{
 			Builder: "windows-arm64-11",
 		},
 	},
+	19: {
+		"linux-386": &Target{
+			Builder:         "linux-386-buster",
+			LongTestBuilder: "linux-386-longtest",
+		},
+		"linux-amd64": &Target{
+			Builder:         "linux-amd64-buster",
+			LongTestBuilder: "linux-amd64-longtest",
+			Race:            true,
+		},
+	},
 }
 
 func init() {