automatically detect BSDs as platform=linuxbsd

(cherry picked from commit 78cd0ffdba6a336475f21be598dca7087a4a66f7)

SConstruct

@@ -195,7 +195,13 @@ elif env_base["p"] != "":
     selected_platform = env_base["p"]
 else:
     # Missing `platform` argument, try to detect platform automatically
-    if sys.platform.startswith("linux"):
+    if (
+        sys.platform.startswith("linux")
+        or sys.platform.startswith("dragonfly")
+        or sys.platform.startswith("freebsd")
+        or sys.platform.startswith("netbsd")
+        or sys.platform.startswith("openbsd")
+    ):
         selected_platform = "x11"
     elif sys.platform == "darwin":
         selected_platform = "osx"