panic_abort: call __rust_abort on xous

Xous does not properly handle invalid instructions. Instead, call
`__rust_abort` and exit normally.

Signed-off-by: Sean Cross <sean@xobs.io>

Author: xobs

library/panic_abort/src/lib.rs

@@ -43,7 +43,8 @@ pub unsafe fn __rust_start_panic(_payload: &mut dyn BoxMeUp) -> u32 {
                 libc::abort();
             }
         } else if #[cfg(any(target_os = "hermit",
-                            all(target_vendor = "fortanix", target_env = "sgx")
+                            all(target_vendor = "fortanix", target_env = "sgx"),
+                            target_os = "xous"
         ))] {
             unsafe fn abort() -> ! {
                 // call std::sys::abort_internal