codegen_llvm_back: simplify a conversion to char

src/librustc_codegen_llvm/back/link.rs

@@ -806,7 +806,7 @@ fn escape_string(s: &[u8]) -> String {
                         let mut x = "Non-UTF-8 output: ".to_string();
                         x.extend(s.iter()
                                   .flat_map(|&b| ascii::escape_default(b))
-                                  .map(|b| char::from_u32(b as u32).unwrap()));
+                                  .map(char::from));
                         x
                     })
             }