title: wasm-pack build report error: could not compile `net2`
body: <p>i use try to use rustwasm refered <a href="https://rustwasm.github.io/book/game-of-life/hello-world.html,all" rel="nofollow noreferrer">https://rustwasm.github.io/book/game-of-life/hello-world.html,all</a> worked fine.
  but when i add <code>reqwest =  "0.9.22"</code> to Cargo.toml,then execute <code>wasm-pack build</code> command in my project,the compiler reports such an error:</p>
  
  <pre><code>$ wasm-pack build &gt; log.log
  [INFO]: Checking for the Wasm target...
  [INFO]: Compiling to Wasm...
  Compiling net2 v0.2.33
  Compiling openssl-sys v0.9.53
  Compiling http v0.1.21
  Compiling string v0.2.1
  Compiling tokio-buf v0.1.1
  Compiling backtrace v0.3.40
  Compiling mime_guess v2.0.1
  Compiling cookie v0.12.0
  error[E0432]: unresolved import sys
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\tcp.rs:18:5
  |
  18 | use sys::c;
  | ^^^ maybe a missing crate sys?
  
  error[E0432]: unresolved import sys
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\udp.rs:18:5
  |
  18 | use sys::c;
  | ^^^ maybe a missing crate sys?
  
  error[E0432]: unresolved import sys
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\socket.rs:22:5
  |
  22 | use sys;
  | ^^^ no sys in the root
  
  error[E0432]: unresolved import sys
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\socket.rs:23:5
  |
  23 | use sys::c;
  | ^^^ maybe a missing crate sys?
  
  error[E0432]: unresolved import sys
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\ext.rs:19:5
  |
  19 | use sys;
  | ^^^ no sys in the root
  
  error[E0432]: unresolved import sys
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\ext.rs:20:5
  |
  20 | use sys::c;
  | ^^^ maybe a missing crate sys?
  
  error[E0412]: cannot find type c_uint in this scope
  --&gt; D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\ext.rs:1335:39
  |
  1335 | fn to_ipv6mr_interface(value: u32) -&gt; c_uint {
  | ^^^^^^ not found in this scope
  help: possible candidate is found in another module, you can import it into scope
  |
  13 | use std::os::raw::c_uint;
  error[E0599]: no method named as_sock found for type &amp;udp::UdpBuilder in the current scope
  </code></pre>
  
  <p>... omit similar error
      --> D:\cargo\registry\src\github.com-1ecc6299db9ec823\net2-0.2.33\src\ext.rs:1499:22
      |
      1499 | get_opt(self.as_sock(), SOL_SOCKET, SO_ERROR).map(int2err)
      | ^^^^^^^ method not found in &amp;udp::UdpBuilder
      |
      = help: items from traits can only be used if the trait is implemented and in scope
      = note: the following trait defines an item as_sock, perhaps you need to implement it:
      candidate #1: ext::AsSock</p>
  
  <pre><code>error: aborting due to 317 previous errors
  
  Some errors have detailed explanations: E0046, E0412, E0422, E0425, E0432, E0599.
  For more information about an error, try rustc --explain E0046.
  error: could not compile net2.
  warning: build failed, waiting for other jobs to finish...
  error: build failed
  Error: Compiling your crate to WebAssembly failed
  Caused by: failed to execute cargo build: exited with exit code: 101
  </code></pre>
  
  <p>my environment</p>
  
  <pre><code>wasm-pack version: wasm-pack 0.8.1
  rustc version: rustc 1.39.0 (4560ea788 2019-11-04)
  operation system: windows10
  </code></pre>