ADDED   build/test/tests/12-threads.tcl
Index: build/test/tests/12-threads.tcl
==================================================================
--- build/test/tests/12-threads.tcl
+++ build/test/tests/12-threads.tcl
@@ -0,0 +1,25 @@
+#! /usr/bin/env tclsh
+
+set buildflags [split [lindex $argv 1] -]
+
+if {$tcl_version == "8.6"} {
+	if {[lsearch -exact $buildflags "unthreaded"] == -1} {
+		set isthreaded 1
+	} else {
+		set isthreaded 0
+	}
+} else {
+	if {[lsearch -exact $buildflags "threaded"] == -1} {
+		set isthreaded 0
+	} else {
+		set isthreaded 1
+	}
+}
+
+if {!$isthreaded} {
+	exit 0
+}
+
+package require Thread
+
+exit 0