Fixing windows compilation bugs

Author: DoeringChristian

include/drjit/custom.h

@@ -20,6 +20,7 @@
 
 #include <nanobind/intrusive/counter.h>
 #include <nanobind/intrusive/ref.h>
+#include <drjit/traversable_base.h>
 
 NAMESPACE_BEGIN(drjit)
 NAMESPACE_BEGIN(detail)

include/drjit/traversable_base.h

@@ -77,7 +77,7 @@ NAMESPACE_END(detail)
  * in the function ``drjit::registry_put`` that takes a ``TraversableBase`` for
  * the pointer argument.
  */
-struct DRJIT_EXPORT TraversableBase : public nanobind::intrusive_base {
+struct DRJIT_EXTRA_EXPORT TraversableBase : public nanobind::intrusive_base {
     /**
      * \brief Traverse all jit arrays in this c++ object. For every jit
      *     variable, the callback should be called, with the provided payload