feat(sled): Print a clear error message when attempting to build on wasm

crates/matrix-sdk-sled/build.rs

@@ -0,0 +1,17 @@
+use std::{env, process};
+
+fn main() {
+    let target_arch = env::var_os("CARGO_CFG_TARGET_ARCH");
+    if target_arch.map_or(false, |arch| arch == "wasm32") {
+        let err = "this crate does not support the target arch 'wasm32'";
+        eprintln!(
+            "\n\
+            ┏━━━━━━━━{pad}━┓\n\
+            ┃ error: {err} ┃\n\
+            ┗━━━━━━━━{pad}━┛\n\
+            ",
+            pad = "━".repeat(err.len()),
+        );
+        process::exit(1);
+    }
+}