commandserver: fix ui.system on Windows

Summary:
The `cmd.exe` does not use the "common" argv[] parsing [1] [2]. For example, the Rust code:

  Command::new("cmd.exe").arg("/c").arg(r#"notepad "a b.txt"#)

will execute (Windows OS command line, as a single string):

  cmd.exe /c "notepad \"a b.txt\""

which will execute:

  notepad \"a b.txt\"

and notepad will complain that the file cannot be found.

To fix it we need to pass the unquoted command and execute either:

  cmd.exe /c "notepad "a b.txt""
  cmd.exe /c notepad "a b.txt"

which will execute:

  notepad "a b.txt"

See also rust-lang/rust#29494.

[1]: https://learn.microsoft.com/en-us/windows/win32/api/shellapi/nf-shellapi-commandlinetoargvw
[2]: https://learn.microsoft.com/en-us/cpp/c-language/parsing-c-command-line-arguments

Reviewed By: zzl0

Differential Revision: D47242639

fbshipit-source-id: c75aa83430520c29002a095333546cc48695244e

eden/scm/lib/commandserver/src/ipc.rs

@@ -59,8 +59,15 @@ impl Client {
             } else {
                 Command::new("/bin/sh")
             };
-            cmd.arg(if cfg!(windows) { "/c" } else { "-c" })
-                .arg(command);
+            #[cfg(windows)]
+            {
+                use std::os::windows::process::CommandExt;
+                cmd.arg("/c").raw_arg(command);
+            }
+            #[cfg(not(windows))]
+            {
+                cmd.arg("-c").arg(command);
+            }
             cmd
         } else {
             Command::new(command)