Fix missing sources and macro redefinition

build/Jamfile.v2

@@ -9,6 +9,10 @@
 
 import ../../config/checks/config : requires ;
 
+project boost/random ;
+
+local SOURCES = random_device.cpp ;
+
 lib boost_random
 
   # Sources

src/random_device.cpp

@@ -10,7 +10,9 @@
  *
  */
 
-#define BOOST_RANDOM_SOURCE
+#ifndef BOOST_RANDOM_SOURCE
+#  define BOOST_RANDOM_SOURCE
+#endif
 
 #include <boost/random/random_device.hpp>
 #include <boost/config.hpp>