> Which compiler needs more than "abort();" in a default statement? gcc and clang don't.

Again, I'm not sure that bpo-28152 is directly related to this issue, but here an example:

$ git diff

diff --git a/Parser/grammar.c b/Parser/grammar.c
index 75fd5b9cde..2b7da68929 100644
--- a/Parser/grammar.c
+++ b/Parser/grammar.c
@@ -139,13 +139,6 @@ findlabel(labellist *ll, int type, const char *str)
     }
     fprintf(stderr, "Label %d/'%s' not found\n", type, str);
     Py_FatalError("grammar.c:findlabel()");
-
-    /* Py_FatalError() is declared with __attribute__((__noreturn__)).
-       GCC emits a warning without "return 0;" (compiler bug!), but Clang is
-       smarter and emits a warning on the return... */
-#ifndef __clang__
-    return 0; /* Make gcc -Wall happy */
-#endif
 }
 
 /* Forward */

$ make

Parser/grammar.c: In function '_Py_findlabel':
Parser/grammar.c:142:1: warning: control reaches end of non-void function [-Wreturn-type]