IRGen: ensure that declarations are not COMDATed

Unfortunately, declarations cannot be marked with their COMDAT groups.
This fixes multithreaded IRGen where we would emit declarations for the
global initializers with COMDATs causing the IR Verifier to object.  The
existing test cases cover this scenario.

Author: compnerd

lib/IRGen/GenDecl.cpp

@@ -1903,6 +1903,8 @@ Address IRGenModule::getAddrOfSILGlobalVariable(SILGlobalVariable *var,
     /// Add a zero initializer.
     if (forDefinition)
       gvar->setInitializer(llvm::Constant::getNullValue(storageTypeWithContainer));
+    else
+      gvar->setComdat(nullptr);
   }
   llvm::Constant *addr = gvar;
   if (var->isInitializedObject()) {
@@ -2184,8 +2186,11 @@ llvm::Function *IRGenModule::getAddrOfSILFunction(
   // associated with it.  The combination of the two allows us to identify the
   // @_silgen_name functions.  These are locally defined function thunks used in
   // the standard library.  Do not give them DLLImport DLL Storage.
-  if (useDllStorage() && f->hasCReferences() && !forDefinition)
-    fn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
+  if (!forDefinition) {
+    fn->setComdat(nullptr);
+    if (f->hasCReferences())
+      fn->setDLLStorageClass(llvm::GlobalValue::DefaultStorageClass);
+  }
 
   // If we have an order number for this function, set it up as appropriate.
   if (hasOrderNumber) {