Build with newer Boost. From Fedora.

Index: gnuradio-runtime/lib/block.cc
--- gnuradio-runtime/lib/block.cc.orig
+++ gnuradio-runtime/lib/block.cc
@@ -34,6 +34,8 @@
 
 namespace gr {
 
+using namespace boost::placeholders;
+
 block::block(const std::string& name,
              io_signature::sptr input_signature,
              io_signature::sptr output_signature)