disable async_process_no_io_safety for nightly

work-around for
smol-rs/polling#38
breaking namada tooling build with nightly 2022-05-20

Author: tzemanovic

Cargo.toml

@@ -22,6 +22,7 @@ once_cell = "1.4.1"
 
 [build-dependencies]
 autocfg = "1"
+rustversion = "1.0.9"
 
 [target.'cfg(unix)'.dependencies]
 async-io = "1.0.0"

build.rs

@@ -10,7 +10,8 @@ fn main() {
         }
     };
 
-    if !cfg.probe_rustc_version(1, 63) {
+    let is_nightly = rustversion::cfg!(nightly);
+    if !cfg.probe_rustc_version(1, 63) || is_nightly {
         autocfg::emit("async_process_no_io_safety");
     }
 }