Importing rustc-1.48.0

Bug: 173721343
Change-Id: Ie8184d9a685086ca8a77266d6c608843f40dc9e1
diff --git a/library/std/src/sys/wasi/fd.rs b/library/std/src/sys/wasi/fd.rs
index 8458ded..ba66eba 100644
--- a/library/std/src/sys/wasi/fd.rs
+++ b/library/std/src/sys/wasi/fd.rs
@@ -1,3 +1,4 @@
+#![deny(unsafe_op_in_unsafe_fn)]
 #![allow(dead_code)]
 
 use super::err2io;