cmd/dist: enforce the lowest bootstrap version

The go1.24 release notes say that go1.22.6 is the
minimum bootstraps required,
the go team also use go1.22.6 bootstraps in testing,
so if there's a problem with using an older version,
automated testing won't uncover it.

Now enforce this in dist to avoid
release notes that do not match reality, which can be confusing.

For golang#64751

Change-Id: I8d50770e19f7f014e1316f0ac872e288a27c20fe

src/cmd/dist/buildtool.go

@@ -123,6 +123,8 @@ var tryDirs = []string{
 	"go1.22.6",
 }
 
+var minBootStrapVersion [3]string = [3]string{"1", "22", "6"}
+
 func bootstrapBuildTools() {
 	goroot_bootstrap := os.Getenv("GOROOT_BOOTSTRAP")
 	if goroot_bootstrap == "" {
@@ -134,6 +136,19 @@ func bootstrapBuildTools() {
 			}
 		}
 	}
+
+	// check bootstrap version.
+	ver := run(pathf("%s/bin", goroot_bootstrap), CheckExit, pathf("%s/bin/go", goroot_bootstrap), "version")
+	_, after, _ := strings.Cut(ver, "go1")
+	if after != "" {
+		v := strings.Split(after, ".")
+		if len(v) > 2 {
+			if v[0] < minBootStrapVersion[1] || v[1] < minBootStrapVersion[2] {
+				fatalf("requires Go 1.%s.%s or later for bootstrap", minBootStrapVersion[1], minBootStrapVersion[2])
+			}
+		}
+	}
+
 	xprintf("Building Go toolchain1 using %s.\n", goroot_bootstrap)
 
 	mkbuildcfg(pathf("%s/src/internal/buildcfg/zbootstrap.go", goroot))