Swap infinite loops for unreachable_unchecked()

Author: adamgreig

asm.s

@@ -120,7 +120,6 @@ __sev:
   .thumb_func
 __udf:
   udf
-  bx lr
 
   .section .text.__wfe
   .global __wfe

bin/thumbv6m-none-eabi.a

@@ -91,7 +91,7 @@ pub fn udf() -> ! {
         #[cfg(all(cortex_m, feature = "inline-asm"))]
         () => unsafe {
             asm!("udf" :::: "volatile");
-            loop { continue }
+            core::hint::unreachable_unchecked();
         },
 
         #[cfg(all(cortex_m, not(feature = "inline-asm")))]
@@ -102,7 +102,7 @@ pub fn udf() -> ! {
 
             __udf();
 
-            loop { continue }
+            core::hint::unreachable_unchecked();
         },
 
         #[cfg(not(cortex_m))]