Format libstd/sys with rustfmt

This commit applies rustfmt with rust-lang/rust's default settings to
files in src/libstd/sys *that are not involved in any currently open PR*
to minimize merge conflicts. THe list of files involved in open PRs was
determined by querying GitHub's GraphQL API with this script:
https://gist.github.com/dtolnay/aa9c34993dc051a4f344d1b10e4487e8

With the list of files from the script in outstanding_files, the
relevant commands were:

    $ find src/libstd/sys -name '*.rs' \
        | xargs rustfmt --edition=2018 --unstable-features --skip-children
    $ rg libstd/sys outstanding_files | xargs git checkout --

Repeating this process several months apart should get us coverage of
most of the rest of the files.

To confirm no funny business:

    $ git checkout $THIS_COMMIT^
    $ git show --pretty= --name-only $THIS_COMMIT \
        | xargs rustfmt --edition=2018 --unstable-features --skip-children
    $ git diff $THIS_COMMIT  # there should be no difference

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libstd/sys/wasm/os.rs b/src/libstd/sys/wasm/os.rs
index 890049e8bfa..193c3892743 100644
--- a/src/libstd/sys/wasm/os.rs
+++ b/src/libstd/sys/wasm/os.rs
@@ -1,5 +1,5 @@
 use crate::error::Error as StdError;
-use crate::ffi::{OsString, OsStr};
+use crate::ffi::{OsStr, OsString};
 use crate::fmt;
 use crate::io;
 use crate::path::{self, PathBuf};
@@ -39,7 +39,9 @@ impl<'a> Iterator for SplitPaths<'a> {
 pub struct JoinPathsError;
 
 pub fn join_paths<I, T>(_paths: I) -> Result<OsString, JoinPathsError>
-    where I: Iterator<Item=T>, T: AsRef<OsStr>
+where
+    I: Iterator<Item = T>,
+    T: AsRef<OsStr>,
 {
     Err(JoinPathsError)
 }