Print to stderr after flushing stdout

In some case, you can get the error message before the greeting message. Let's flush stdout before writing an error message to avoid confusion when reading the output.

Fixes #413 (closed).

src/error.h

@@ -50,6 +50,7 @@
 extern int engine_rank;
 #define error(s, ...)                                                      \
   ({                                                                       \
+    fflush(stdout);                                                        \
     fprintf(stderr, "[%04i] %s %s:%s():%i: " s "\n", engine_rank,          \
             clocks_get_timesincestart(), __FILE__, __FUNCTION__, __LINE__, \
             ##__VA_ARGS__);                                                \
@@ -58,6 +59,7 @@ extern int engine_rank;
 #else
 #define error(s, ...)                                                      \
   ({                                                                       \
+    fflush(stdout);                                                        \
     fprintf(stderr, "%s %s:%s():%i: " s "\n", clocks_get_timesincestart(), \
             __FILE__, __FUNCTION__, __LINE__, ##__VA_ARGS__);              \
     swift_abort(1);                                                        \
@@ -72,6 +74,7 @@ extern int engine_rank;
  */
 #define mpi_error(res, s, ...)                                             \
   ({                                                                       \
+    fflush(stdout);                                                        \
     fprintf(stderr, "[%04i] %s %s:%s():%i: " s "\n", engine_rank,          \
             clocks_get_timesincestart(), __FILE__, __FUNCTION__, __LINE__, \
             ##__VA_ARGS__);                                                \
@@ -84,6 +87,7 @@ extern int engine_rank;
 
 #define mpi_error_string(res, s, ...)                                      \
   ({                                                                       \
+    fflush(stdout);                                                        \
     fprintf(stderr, "[%04i] %s %s:%s():%i: " s "\n", engine_rank,          \
             clocks_get_timesincestart(), __FILE__, __FUNCTION__, __LINE__, \
             ##__VA_ARGS__);                                                \
@@ -122,6 +126,7 @@ extern int engine_rank;
 #define assert(expr)                                                          \
   ({                                                                          \
     if (!(expr)) {                                                            \
+      fflush(stdout);                                                         \
       fprintf(stderr, "[%04i] %s %s:%s():%i: FAILED ASSERTION: " #expr " \n", \
               engine_rank, clocks_get_timesincestart(), __FILE__,             \
               __FUNCTION__, __LINE__);                                        \
@@ -133,6 +138,7 @@ extern int engine_rank;
 #define assert(expr)                                                          \
   ({                                                                          \
     if (!(expr)) {                                                            \
+      fflush(stdout);                                                         \
       fprintf(stderr, "%s %s:%s():%i: FAILED ASSERTION: " #expr " \n",        \
               clocks_get_timesincestart(), __FILE__, __FUNCTION__, __LINE__); \
       fflush(stderr);                                                         \