🩹 explicitly export the RealNumber constants

Signed-off-by: burgholzer <burgholzer@me.com>
Signed-off-by: Lukas Burgholzer <burgholzer@me.com>
Signed-off-by: burgholzer <burgholzer@me.com>

include/mqt-core/dd/RealNumber.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "dd/DDDefinitions.hpp"
+#include "mqt_core_dd_export.h"
 
 #include <istream>
 #include <limits>
@@ -230,11 +231,11 @@ struct RealNumber {
 namespace constants {
 // NOLINTBEGIN(cppcoreguidelines-avoid-non-const-global-variables)
 /// The constant zero.
-extern RealNumber zero;
+MQT_CORE_DD_EXPORT extern RealNumber zero;
 /// The constant one.
-extern RealNumber one;
+MQT_CORE_DD_EXPORT extern RealNumber one;
 /// The constant sqrt(2)/2 = 1/sqrt(2).
-extern RealNumber sqrt2over2;
+MQT_CORE_DD_EXPORT extern RealNumber sqrt2over2;
 // NOLINTEND(cppcoreguidelines-avoid-non-const-global-variables)
 
 /**