Always use -L$(QTDIR)/lib when looking for -lqt. This means that QTDIR must be set when building.

configure.in

@@ -482,9 +482,12 @@ fi
 
 res=`echo :$MOZ_FE | grep -c " qt"`
 if [ test $res != 0 ]; then
+    _SAVE_LDFLAGS=$LDFLAGS
+    LDFLAGS="$LDFLAGS -L$QTDIR/lib"
     AC_CHECK_LIB(qt, set_new_handler, 
 	[FE_QT_LIBS="-lqt" FE_QT_CFLAGS='-I$(QTDIR)/include'],
 	[MISSING_QT=1])
+    LDFLAGS=$_SAVE_LDFLAGS 
     AC_PATH_PROG(MOC, moc, /bin/true)
 fi