Disable unreliable assertion for external frame unwinding.

Broken on Fedora/ARM64. Reported by Yichun Zhang.

src/lj_err.c

@@ -482,7 +482,9 @@ void lj_err_verify(void)
 {
   struct dwarf_eh_bases ehb;
   lj_assertX(_Unwind_Find_FDE((void *)lj_err_throw, &ehb), "broken build: external frame unwinding enabled, but missing -funwind-tables");
+  /* Check disabled, because of broken Fedora/ARM64. See #722.
   lj_assertX(_Unwind_Find_FDE((void *)_Unwind_RaiseException, &ehb), "broken build: external frame unwinding enabled, but system libraries have no unwind tables");
+  */
 }
 #endif