[clang][bytecode] Fix emitDestruction() for dummy descriptors (#134665)

This might happen if the referenced declaration is invalid and thus gets
a dummy descriptor. We ran into an assertion later on.

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -6801,6 +6801,10 @@ bool Compiler<Emitter>::emitDestruction(const Descriptor *Desc,
   assert(!Desc->isPrimitive());
   assert(!Desc->isPrimitiveArray());
 
+  // Can happen if the decl is invalid.
+  if (Desc->isDummy())
+    return true;
+
   // Arrays.
   if (Desc->isArray()) {
     const Descriptor *ElemDesc = Desc->ElemDesc;

clang/test/AST/ByteCode/cxx17.cpp

@@ -125,3 +125,14 @@ namespace constant {
   }
   static_assert(f());
 }
+
+
+template <int a> struct i; // both-note {{template is declared here}}
+template <> struct i<0> {};
+
+template <int x> constexpr auto c() {
+  i<x> g; // both-error {{implicit instantiation of undefined template 'i<1>'}}
+  return 0;
+}
+
+auto y = c<1>(); // both-note {{in instantiation of function template specialization 'c<1>' requested here}}