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

src/libstd/sys/windows/stdio_uwp.rs

@@ -1,12 +1,11 @@
 #![unstable(issue = "0", feature = "windows_stdio")]
 
 use crate::io;
+use crate::mem::ManuallyDrop;
 use crate::sys::c;
 use crate::sys::handle::Handle;
-use crate::mem::ManuallyDrop;
 
-pub struct Stdin {
-}
+pub struct Stdin {}
 pub struct Stdout;
 pub struct Stderr;
 
@@ -32,7 +31,7 @@ fn write(handle_id: c::DWORD, data: &[u8]) -> io::Result<usize> {
 
 impl Stdin {
     pub fn new() -> io::Result<Stdin> {
-        Ok(Stdin { })
+        Ok(Stdin {})
     }
 }