feat: gate enhanced Wasm support on tokio_unstable

Signed-off-by: Richard Zak <richard@profian.com>

tokio/src/lib.rs

@@ -393,6 +393,10 @@ compile_error! {
     "Tokio requires the platform pointer width to be 32, 64, or 128 bits"
 }
 
+#[cfg(not(tokio_unstable))]
+#[cfg(wasm, any(feature = "fs", feature = "io-std", feature = "net", feature = "process", feature = "rt-multi-thread", feature = "signal", feature = "time"))]
+compile_error!("Only features sync,macros,io-util,rt are supported on wasm.");
+
 // Includes re-exports used by macros.
 //
 // This module is not intended to be part of the public API. In general, any