Implement DPI import/export as loose functions

src/V3Life.cpp

@@ -414,7 +414,7 @@ private:
         // UINFO(4, "  CFUNC " << nodep << endl);
         if (!m_tracingCall && !nodep->entryPoint()) return;
         m_tracingCall = false;
-        if (nodep->dpiImport() && !nodep->pure()) {
+        if (nodep->dpiImportPrototype() && !nodep->pure()) {
             m_sideEffect = true;  // If appears on assign RHS, don't ever delete the assignment
         }
         iterateChildren(nodep);