__assert_fail(): remove _Noreturn, to get proper stacktraces

for _Noreturn functions, gcc generates code that trashes the
stack frame, and so it makes it impossible to inspect the causes
of an assert error in gdb.

abort() is not affected (i have not yet investigated why).

include/assert.h

@@ -12,7 +12,7 @@
 extern "C" {
 #endif
 
-_Noreturn void __assert_fail (const char *, const char *, int, const char *);
+void __assert_fail (const char *, const char *, int, const char *);
 
 #ifdef __cplusplus
 }

src/exit/assert.c

@@ -1,7 +1,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-_Noreturn void __assert_fail(const char *expr, const char *file, int line, const char *func)
+void __assert_fail(const char *expr, const char *file, int line, const char *func)
 {
 	fprintf(stderr, "Assertion failed: %s (%s: %s: %d)\n", expr, file, func, line);
 	fflush(NULL);