cmd/buildlet: enable developer mode on macOS

Fixes golang/go#31123

Change-Id: Ib510969ffbedad8f1690b6e62e5cce6d49022860
Reviewed-on: https://go-review.googlesource.com/c/build/+/170339
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
diff --git a/cmd/buildlet/buildlet.go b/cmd/buildlet/buildlet.go
index a58998a..2c9971e 100644
--- a/cmd/buildlet/buildlet.go
+++ b/cmd/buildlet/buildlet.go
@@ -1656,6 +1656,10 @@
 
 	disableMacScreensaver()
 
+	// Enable developer mode for runtime tests. (Issue 31123)
+	// Best effort; ignore any error.
+	exec.Command("/usr/sbin/DevToolsSecurity", "-enable").Run()
+
 	version, err := exec.Command("sw_vers", "-productVersion").Output()
 	if err != nil {
 		log.Fatalf("failed to find sw_vers -productVersion: %v", err)