Add OS constraint values for DragonFlyBSD, Redox, and Illumos

Author: jmillikin

os/BUILD

@@ -28,6 +28,11 @@ constraint_value(
     constraint_setting = ":os",
 )
 
+constraint_value(
+    name = "dragonflybsd",
+    constraint_setting = ":os",
+)
+
 constraint_value(
     name = "haiku",
     constraint_setting = ":os",
@@ -132,3 +137,13 @@ constraint_value(
     name = "uefi",
     constraint_setting = ":os",
 )
+
+constraint_value(
+    name = "redox",
+    constraint_setting = ":os",
+)
+
+constraint_value(
+    name = "illumos",
+    constraint_setting = ":os",
+)