replace | with || in {unsigned_int}::carrying_add

Using short-circuiting operators makes it easier to perform some kinds
of source code analysis, like MC/DC code coverage (a requirement in
safety-critical environments). The optimized x86_64 assembly is the same
between the old and new versions:

```
mov eax, edi
add dl, -1
adc eax, esi
setb dl
ret
```

Author: pietroalbini

library/core/src/num/uint_macros.rs

@@ -1525,7 +1525,7 @@ macro_rules! uint_impl {
             //   to generate optimal code for now, and LLVM doesn't have an equivalent intrinsic
             let (a, b) = self.overflowing_add(rhs);
             let (c, d) = a.overflowing_add(carry as $SelfT);
-            (c, b | d)
+            (c, b || d)
         }
 
         /// Calculates `self` + `rhs` with a signed `rhs`