Indent the #error directives so a classic K&R cpp doesn't see them.

Python/compile.c

@@ -63,13 +63,13 @@ PERFORMANCE OF THIS SOFTWARE.
    (which defines too many confusing symbols), but we can check here
    that they haven't changed (which is very unlikely, but possible). */
 #if Py_single_input != single_input
-#error "single_input has changed -- update Py_single_input in Python.h"
+  #error "single_input has changed -- update Py_single_input in Python.h"
 #endif
 #if Py_file_input != file_input
-#error "file_input has changed -- update Py_file_input in Python.h"
+  #error "file_input has changed -- update Py_file_input in Python.h"
 #endif
 #if Py_eval_input != eval_input
-#error "eval_input has changed -- update Py_eval_input in Python.h"
+  #error "eval_input has changed -- update Py_eval_input in Python.h"
 #endif
 
 int Py_OptimizeFlag = 0;