From gah@grenache.mhcnet.att.com (George A. Howlett) we get
the answer:

Instead of adding TclX to blt_wish, try it the other way.  Add
BLT to wishx.  It`s pretty simple.
 
In the file ./tksrc/tkXAppInit.c, add the a call to the BLT
initialization routine right after line 116.
 
    if (TkX_Init(interp) == TCL_ERROR) {
        return TCL_ERROR;
    }
    if (Blt_Init(interp) != TCL_OK)) {
        return TCL_ERROR;
    }
 
Link wishx with libBLT.a and that`s it.
 
Others recommend the tkmkmf or make-a-wish packages.