native, rustuv: Fix spawning with empty args

There was a bug in both libnative and libuv which prevented child processes from
being spawned correctly on windows when one of the arguments was an empty
string. The libuv bug has since been fixed upstream, and the libnative bug was
fixed as part of this commit.

When updating libuv, this also includes a fix for #15149.

Closes #15149
Closes #16272

src/libnative/io/process.rs

@@ -479,7 +479,10 @@ fn make_command_line(prog: &CString, args: &[CString]) -> String {
     return cmd;
 
     fn append_arg(cmd: &mut String, arg: &str) {
-        let quote = arg.chars().any(|c| c == ' ' || c == '\t');
+        // If an argument has 0 characters then we need to quote it to ensure
+        // that it actually gets passed through on the command line or otherwise
+        // it will be dropped entirely when parsed on the other end.
+        let quote = arg.chars().any(|c| c == ' ' || c == '\t') || arg.len() == 0;
         if quote {
             cmd.push_char('"');
         }