Fix ICE when using asm! on an unsupported architecture

Fixes #75220

Author: Amanieu

src/librustc_ast_lowering/expr.rs

@@ -1067,7 +1067,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             .collect();
 
         // Stop if there were any errors when lowering the register classes
-        if operands.len() != asm.operands.len() {
+        if operands.len() != asm.operands.len() || sess.asm_arch.is_none() {
             return hir::ExprKind::Err;
         }
 

src/test/ui/asm/bad-arch.rs

@@ -0,0 +1,18 @@
+// compile-flags: --target wasm32-unknown-unknown
+
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+    () => {};
+}
+#[lang = "sized"]
+trait Sized {}
+
+fn main() {
+    unsafe {
+        asm!("");
+        //~^ ERROR asm! is unsupported on this target
+    }
+}

src/test/ui/asm/bad-arch.stderr

@@ -0,0 +1,8 @@
+error[E0472]: asm! is unsupported on this target
+  --> $DIR/bad-arch.rs:15:9
+   |
+LL |         asm!("");
+   |         ^^^^^^^^^
+
+error: aborting due to previous error
+

src/test/ui/feature-gates/feature-gate-asm.rs

@@ -1,4 +1,4 @@
-// ignore-emscripten
+// only-x86_64
 
 fn main() {
     unsafe {

src/test/ui/feature-gates/feature-gate-asm2.rs

@@ -1,4 +1,4 @@
-// ignore-emscripten
+// only-x86_64
 
 fn main() {
     unsafe {