src/Pure/System/platform.scala

--- a/src/Pure/System/platform.scala	Thu Apr 22 23:03:58 2021 +0200
+++ b/src/Pure/System/platform.scala	Thu Apr 22 23:40:22 2021 +0200
@@ -14,6 +14,7 @@
   val is_linux: Boolean = System.getProperty("os.name", "") == "Linux"
   val is_macos: Boolean = System.getProperty("os.name", "") == "Mac OS X"
   val is_windows: Boolean = System.getProperty("os.name", "").startsWith("Windows")
+  val is_unix: Boolean = is_linux || is_macos
 
   def family: Family.Value =
     if (is_linux) Family.linux