Rollup merge of #130554 - ShE3py:unsupported-exitcode, r=Noratrieb

`pal::unsupported::process::ExitCode`: use an `u8` instead of a `bool`

`ExitCode` should “represents the status code the current process can return to its parent under normal termination”, but is currently represented as a `bool` on unsupported platforms, making the `impl From<u8> for ExitCode` lossy.

Fixes #130532.

History: [IRLO thread](https://internals.rust-lang.org/t/mini-pre-rfc-redesigning-process-exitstatus/5426) (`ExitCode` as a `main` return), #48618 (initial impl), #93445 (`From<u8>` impl).

library/std/src/sys/pal/unsupported/process.rs

@@ -255,11 +255,11 @@ impl ExitStatusError {
 }
 
 #[derive(PartialEq, Eq, Clone, Copy, Debug)]
-pub struct ExitCode(bool);
+pub struct ExitCode(u8);
 
 impl ExitCode {
-    pub const SUCCESS: ExitCode = ExitCode(false);
-    pub const FAILURE: ExitCode = ExitCode(true);
+    pub const SUCCESS: ExitCode = ExitCode(0);
+    pub const FAILURE: ExitCode = ExitCode(1);
 
     pub fn as_i32(&self) -> i32 {
         self.0 as i32
@@ -268,10 +268,7 @@ impl ExitCode {
 
 impl From<u8> for ExitCode {
     fn from(code: u8) -> Self {
-        match code {
-            0 => Self::SUCCESS,
-            1..=255 => Self::FAILURE,
-        }
+        Self(code)
     }
 }