Merge pull request #71 from aiuto/vos

Add Apple visionos.
diff --git a/os/BUILD b/os/BUILD
index e0484ee..1d9fedb 100644
--- a/os/BUILD
+++ b/os/BUILD
@@ -83,6 +83,11 @@
 )
 
 constraint_value(
+    name = "visionos",
+    constraint_setting = ":os",
+)
+
+constraint_value(
     name = "qnx",
     constraint_setting = ":os",
 )