Not redefining BOOST macro when boost is included before bob.core/random.h

bob/core/include/bob.core/boost/integer_log2.hpp

@@ -23,6 +23,7 @@ namespace core {
 namespace random {
 namespace detail {
 
+#ifndef BOOST_RANDOM_DETAIL_CONSTEXPR
 #if !defined(BOOST_NO_CXX11_CONSTEXPR)
 #define BOOST_RANDOM_DETAIL_CONSTEXPR constexpr
 #elif defined(BOOST_MSVC)
@@ -32,6 +33,7 @@ namespace detail {
 #else
 #define BOOST_RANDOM_DETAIL_CONSTEXPR inline
 #endif
+#endif
 
 template<int Shift>
 struct integer_log2_impl