Add NORETURN to __fatal_error

stmhal/main.c

@@ -85,7 +85,7 @@ void flash_error(int n) {
     led_state(PYB_LED_R2, 0);
 }
 
-void __fatal_error(const char *msg) {
+void NORETURN __fatal_error(const char *msg) {
     for (volatile uint delay = 0; delay < 10000000; delay++) {
     }
     led_state(1, 1);
@@ -115,7 +115,6 @@ void MP_WEAK __assert_func(const char *file, int line, const char *func, const c
     (void)func;
     printf("Assertion '%s' failed, at file %s:%d\n", expr, file, line);
     __fatal_error("");
-    while (1);
 }
 #endif