Make the wasm_c_abi future compat warning a hard error

This is the next step in getting rid of the broken C abi for
wasm32-unknown-unknown.

compiler/rustc_metadata/messages.ftl

@@ -290,6 +290,9 @@ metadata_unsupported_abi =
 metadata_unsupported_abi_i686 =
     ABI not supported by `#[link(kind = "raw-dylib")]` on i686
 
+metadata_wasm_c_abi =
+    older versions of the `wasm-bindgen` crate are incompatible with current versions of Rust; please update to `wasm-bindgen` v0.2.88
+
 metadata_wasm_import_form =
     wasm import module must be of the form `wasm_import_module = "string"`
 

compiler/rustc_metadata/src/creader.rs

@@ -1076,12 +1076,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
             // Make a point span rather than covering the whole file
             let span = krate.spans.inner_span.shrink_to_lo();
 
-            self.sess.psess.buffer_lint(
-                lint::builtin::WASM_C_ABI,
-                span,
-                ast::CRATE_NODE_ID,
-                BuiltinLintDiag::WasmCAbi,
-            );
+            self.sess.dcx().emit_err(errors::WasmCAbi { span });
         }
     }
 

compiler/rustc_metadata/src/errors.rs

@@ -732,3 +732,10 @@ pub struct ImportNameTypeRaw {
     #[primary_span]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(metadata_wasm_c_abi)]
+pub(crate) struct WasmCAbi {
+    #[primary_span]
+    pub span: Span,
+}