[SILGen] Make sure we emit lazy conformances for @asyncHandlers.

Fixes rdar://73798572.

Author: DougGregor

lib/SILGen/SILGenFunction.cpp

@@ -559,7 +559,8 @@ void SILGenFunction::emitAsyncHandler(FuncDecl *fd) {
   bodyFn->setDebugScope(new (getModule()) SILDebugScope(loc, bodyFn));
 
   SILGenFunction(SGM, *bodyFn, fd).emitFunction(fd);
-  
+  SGM.emitLazyConformancesForFunction(bodyFn);
+
   // 2. step: emit the original asyncHandler function
   //
   Scope scope(*this, loc);

test/SILGen/async_handler_witness_table.swift

@@ -0,0 +1,19 @@
+// RUN: %target-swift-emit-silgen -sdk %S/Inputs -I %S/Inputs -enable-source-import %s -enable-experimental-concurrency > %t.out
+// RUN: %FileCheck -check-prefix=CHECK -check-prefix=CHECK-%target-ptrsize %s < %t.out
+// RUN: %FileCheck -check-prefix=NEGATIVE %s < %t.out
+
+// REQUIRES: objc_interop
+// REQUIRES: concurrency
+
+import gizmo
+
+func hashEm<H: Hashable>(_ x: H) {}
+
+public class A {
+  @asyncHandler
+  public func f() {
+    hashEm(NSRuncingOptions.mince)
+  }
+}
+
+// CHECK: sil_witness_table shared [serialized] NSRuncingOptions: Hashable module gizmo