Handle complex equations in when statements.

Fix for ticket #4157

Belonging to [master]:
  - OpenModelica/OMCompiler#3086

Compiler/Template/CodegenC.tpl

@@ -5687,13 +5687,30 @@ match ty
     else
       error(sourceInfo(), 'No runtime support for this sort of array call: <%cref(left)%> = <%dumpExp(right,"\"")%>')
     end match
+  case T_COMPLEX(varLst = varLst, complexClassType=RECORD(__)) then
+    let &preExp = buffer ""
+    let exp = daeExp(right, context, &preExp, &varDecls, &auxFunction)
+    let tmp = tempDecl(expTypeModelica(ty),&varDecls)
+    <<
+    <%preExp%>
+    <%tmp%> = <%exp%>;
+    <% varLst |> var as TYPES_VAR(__) =>
+      match var.ty
+      case T_ARRAY(__) then
+        copyArrayData(var.ty, '<%tmp%>._<%var.name%>', appendStringCref(var.name,left), context, &preExp, &varDecls, &auxFunction)
+      else
+        let varPart = contextCref(appendStringCref(var.name,left),context, &auxFunction)
+        '<%varPart%> = <%tmp%>._<%var.name%>;'
+    ; separator="\n"
+    %>
+    >>
   else
     let &preExp = buffer ""
     let exp = daeExp(right, context, &preExp, &varDecls, &auxFunction)
     <<
     <%preExp%>
     <%cref(left)%> = <%exp%>;
-   >>
+    >>
 end whenAssign;
 
 template equationIfEquationAssign(SimEqSystem eq, Context context, Text &varDecls, Text &eqnsDecls, String modelNamePrefixStr)