Fixes issue where fdset types cant resolve

[TheNotary]

After cleaning up a sample rust app I've been testing with wasmer, I discovered on the latest version/ branch, the struct for fd_set was throwing errors. It seems that they didn't have the absolute namespace pathing (e.g. ::c_int) and instead were written as c_int.

Error:

$ cargo wasix run
...
error[E0412]: cannot find type c_int in this scope
--> /libc/src/wasi/wasix.rs:272:17
|
272 | __fds: [c_int; FD_SETSIZE as usize],
| ^^^^^ not found in this scope
|
help: consider importing one of these type aliases
|
1 + use c_int;
|
1 + use ffi::c_int;
|
error[E0425]: cannot find value FD_SETSIZE in this scope
--> /libc/src/wasi/wasix.rs:272:24
|
272 | __fds: [c_int; FD_SETSIZE as usize],
| ^^^^^^^^^^ not found in this scope
|
help: consider importing this constant through its public re-export
|
1 + use FD_SETSIZE;
|

I also had a minor issue running the tests, the compiler wanted me to remove unnecessary parentheses around a closure in build.rs so I included that to ensure the build passed in this PR.