Fix unhelpful unused parameter warning in wxX11 wxFontEnumerator

This warning can't really be avoided in this case, unless we decided not
to return any fonts at all if we can't test whether they're monospaced
or not, but this would probably be even less useful.

src/unix/fontenum.cpp

@@ -62,6 +62,10 @@ wxCompareFamilies (const void *a, const void *b)
 bool wxFontEnumerator::EnumerateFacenames(wxFontEncoding encoding,
                                           bool fixedWidthOnly)
 {
+    // This parameter may be unused when pango_font_family_is_monospace() is
+    // not available, suppress the (unavoidable) warning in this case.
+    wxUnusedVar(fixedWidthOnly);
+
     if ( encoding != wxFONTENCODING_SYSTEM && encoding != wxFONTENCODING_UTF8 )
     {
         // Pango supports only UTF-8 encoding (and system means any, so we