small changes following Matthieu's suggestions

examples/main.c

@@ -595,6 +595,11 @@ int main(int argc, char *argv[]) {
   error(
       "Error: Cannot use radiative transfer without GEAR star model for now\n");
 #endif
+#ifdef WITH_MPI
+  /* Temporary, this will be removed in due time */
+  error(
+      "Error: Cannot use radiative transfer with MPI\n");
+#endif
 #endif /* idfef RT_NONE */
 
 /* Let's pin the main thread, now we know if affinity will be used. */

src/rt/debug/rt_io.h

@@ -51,7 +51,7 @@ INLINE static int rt_write_particles(const struct xpart* xparts,
       "RTCallsPair", INT, 1, UNIT_CONV_NO_UNITS, 0, xparts, rt_data.calls_pair,
       "number of calls to this particle during one time step in self task");
 
-  return (5);
+  return 5;
 }
 
 /**
@@ -79,6 +79,6 @@ INLINE static int rt_write_stars(const struct spart* sparts,
       "RTCallsPair", INT, 1, UNIT_CONV_NO_UNITS, 0, sparts, rt_data.calls_pair,
       "number of calls to this particle during one time step in self task");
 
-  return (5);
+  return 5;
 }
 #endif /* SWIFT_RT_IO_DEBUG_H */