tkUnixRFont.c is not used it seems. tkUnixFont.c is instead (I will try to check whether the test still fails with --enable-xft, which I guess should make use of tkUnixRFont.c).

Debugging this a bit, just by running <code>font actual {{DejaVu Sans}}</code>, everything looks OK until:
<verbatim>
(gdb) bt
#0  ListFonts (display=0x6804e0, faceName=0x73a8f0 "DejaVu Sans", numNamesPtr=0x7fffffffd71c) at
#1  0x00007ffff7b549f5 in ListFontOrAlias (display=0x6804e0, faceName=0x73a8f0 "DejaVu Sans", numNamesPtr=0x7fffffffd71c) at
#2  0x00007ffff7b523fb in CreateClosestFont (tkwin=0x667880, faPtr=0x7fffffffd830, xaPtr=0x7fffffffd7d0) at
#3  0x00007ffff7b512a2 in TkpGetFontFromAttributes (tkFontPtr=0x0, tkwin=0x667880, faPtr=0x7fffffffd830) at
#4  0x00007ffff7a017ae in Tk_AllocFontFromObj (interp=0x618ca0, tkwin=0x667880, objPtr=0x65c7e0) at
#5  0x00007ffff7a0027e in Tk_FontObjCmd (clientData=0x667880, interp=0x618ca0, objc=3, objv=0x61cd50) at
#6  0x00007ffff75bdd45 in Dispatch (data=0x65f5d8, interp=0x618ca0, result=0) at
#7  0x00007ffff75bddce in TclNRRunCallbacks (interp=0x618ca0, result=0, rootPtr=0x0) at
#8  0x00007ffff75c0919 in TclEvalObjEx (interp=0x618ca0, objPtr=0x0, flags=131072, invoker=0x0, word=0) at
#9  0x00007ffff75c08af in Tcl_EvalObjEx (interp=0x618ca0, objPtr=0xffffffff, flags=131072) at
#10 0x00007ffff76ae972 in Tcl_RecordAndEvalObj (interp=0x618ca0, cmdPtr=0x661bb0, flags=131072) at
#11 0x00007ffff76ae637 in Tcl_RecordAndEval (interp=0x618ca0, cmd=0x7fffffffdec0 "font actual {{DejaVu Sans}}\n", flags=131072) at
#12 0x00007ffff7a17f78 in StdinProc (clientData=0x7fffffffdea0, mask=2) at
#13 0x00007ffff76c1dff in Tcl_NotifyChannel (channel=0x6eae00, mask=2) at
#14 0x00007ffff773971a in FileHandlerEventProc (evPtr=0x7048e0, flags=-3) at
#15 0x00007ffff76e669f in Tcl_ServiceEvent (flags=-3) at
#16 0x00007ffff76e6adb in Tcl_DoOneEvent (flags=-3) at
#17 0x00007ffff79fe7f2 in Tk_MainLoop () at
#18 0x00007ffff7a17d42 in Tk_MainEx (argc=-1, argv=0x7fffffffe1e0, appInitProc=0x400aeb <Tcl_AppInit>, interp=0x618ca0) at
#19 0x0000000000400ae4 in main (argc=1, argv=0x7fffffffe1d8) at
</verbatim>

ListFonts simply is:
<verbatim>
    sprintf(buf, "-*-%.80s-*-*-*-*-*-*-*-*-*-*-*-*", faceName);
    return XListFonts(display, buf, 10000, numNamesPtr);
</verbatim>

At this point we have:
<verbatim>
(gdb) p faceName
$39 = 0x73a8f0 "DejaVu Sans"
(gdb) p buf
$40 = "-*-DejaVu '\000' <repeats 13 times>,
</verbatim>

The X11 library XListFonts() does not return any font with this (numNamesPtr is zero).