Define _USE_MATH_DEFINES in kernel header

include/aidge/backend/cpu/operator/HeavisideImpl_kernels.hpp

@@ -15,6 +15,7 @@
 #include "aidge/utils/Registrar.hpp"
 
 #include <cstddef> // std::size_t
+#define _USE_MATH_DEFINES
 #include <cmath>
 
 #include "aidge/backend/cpu/operator/HeavisideImpl.hpp"