fix(support_rza1): fix build failure when doing native build

It should compile successfully even on an unsupported target so that
`cargo test --workspace` is useful.

Author: yvt

src/constance_support_rza1/src/stdout.rs

@@ -56,6 +56,7 @@ where
 }
 
 #[inline]
+#[cfg(target_arch = "arm")]
 fn interrupt_free<T>(x: impl FnOnce() -> T) -> T {
     let cpsr: u32;
     unsafe { asm!("mrs {}, cpsr", out(reg)cpsr) };
@@ -72,6 +73,11 @@ fn interrupt_free<T>(x: impl FnOnce() -> T) -> T {
     ret
 }
 
+#[cfg(not(target_arch = "arm"))]
+fn interrupt_free<T>(_: impl FnOnce() -> T) -> T {
+    panic!("this crate is not supported on this platform")
+}
+
 #[doc(hidden)]
 pub fn write_str(s: &str) {
     interrupt_free(|| unsafe {