Build with newer Boost. From Fedora.

Index: gr-qtgui/lib/freq_sink_c_impl.cc
--- gr-qtgui/lib/freq_sink_c_impl.cc.orig
+++ gr-qtgui/lib/freq_sink_c_impl.cc
@@ -38,6 +38,8 @@
 namespace gr {
 namespace qtgui {
 
+using namespace boost::placeholders;
+
 freq_sink_c::sptr freq_sink_c::make(int fftsize,
                                     int wintype,
                                     double fc,
