Add #[inline] to some new functions

Co-authored-by: Camille Gillot <gillot.camille@gmail.com>

compiler/rustc_data_structures/src/hashes.rs

@@ -36,6 +36,7 @@ impl Hash64 {
 }
 
 impl BitXorAssign<u64> for Hash64 {
+    #[inline]
     fn bitxor_assign(&mut self, rhs: u64) {
         self.inner ^= rhs;
     }