without patch below, it would be needed to have
LD_PRELOAD=libpthread.so set when running tcl/tk 
non-threaded FLAVOR

--- tclconfig/tcl.m4.orig	Tue May 14 11:12:51 2013
+++ tclconfig/tcl.m4	Tue May 14 11:14:03 2013
@@ -1593,12 +1593,6 @@ dnl AC_CHECK_TOOL(AR, ar)
 	    AS_IF([test $tcl_cv_ld_elf = yes], [
 		LDFLAGS=-Wl,-export-dynamic
 	    ], [LDFLAGS=""])
-	    AS_IF([test "${TCL_THREADS}" = "1"], [
-		# OpenBSD builds and links with -pthread, never -lpthread.
-		LIBS=`echo $LIBS | sed s/-lpthread//`
-		CFLAGS="$CFLAGS -pthread"
-		SHLIB_CFLAGS="$SHLIB_CFLAGS -pthread"
-	    ])
 	    # OpenBSD doesn't do version numbers with dots.
 	    UNSHARED_LIB_SUFFIX='${TCL_TRIM_DOTS}.a'
 	    TCL_LIB_VERSIONS_OK=nodots