Convert user_api header and user_init source files to valid C code.

PiperOrigin-RevId: 629691192
Change-Id: I9be78aca27ae584fff0b733e9015b2bb3b927ca4

src/xml/xml_native_reader.cc

@@ -3394,7 +3394,7 @@ void mjXReader::Body(XMLElement* section, mjsBody* pbody, mjsFrame* frame) {
 
       // store rotation difference
       mjsOrientation alt;
-      mjs_defaultOrientation(alt);
+      mjs_defaultOrientation(&alt);
       alt.type = mjORIENTATION_EULER;
       mjuu_copyvec(alt.euler, euler, 3);
       double rotation[4] = {1, 0, 0, 0};

src/xml/xml_urdf.cc

@@ -633,7 +633,7 @@ void mjXURDF::Origin(XMLElement* origin_elem, double* pos, double* quat) {
 
     // orientation
     mjsOrientation alt;
-    mjs_defaultOrientation(alt);
+    mjs_defaultOrientation(&alt);
     if (ReadAttr(temp, "rpy", 3, alt.euler, text)) {
       alt.type = mjORIENTATION_EULER;
       mjs_resolveOrientation(quat, 0, "XYZ", &alt);