LTO: Drop comdats when converting definitions to declarations.

llvm/lib/Transforms/IPO/FunctionImport.cpp

llvm::EmitImportsFiles(StringRef ModulePath, StringRef OutputFilename,
   return std::error_code();
 }
 
 void llvm::convertToDeclaration(GlobalValue &GV) {
   DEBUG(dbgs() << "Converting to a declaration: `" << GV.getName() << "\n");
   if (Function *F = dyn_cast<Function>(&GV)) {
     F->deleteBody();
     F->clearMetadata();
+    F->setComdat(nullptr);
   } else if (GlobalVariable *V = dyn_cast<GlobalVariable>(&GV)) {
     V->setInitializer(nullptr);
     V->setLinkage(GlobalValue::ExternalLinkage);
     V->clearMetadata();
+    V->setComdat(nullptr);
   } else
     // For now we don't resolve or drop aliases. Once we do we'll
     // need to add support here for creating either a function or
     // variable declaration, and return the new GlobalValue* for
     // the caller to use.
     llvm_unreachable("Expected function or variable");
 }
 

llvm/test/LTO/Resolution/X86/not-prevailing.ll

 ; Check that 'foo' and 'bar' produced as undefined.
 ; SYMBOLS: NOTYPE  GLOBAL DEFAULT  UND bar
 ; SYMBOLS: NOTYPE  GLOBAL DEFAULT  UND foo
 ; SYMBOLS: FUNC    GLOBAL DEFAULT    2 zed
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
 
-define weak i32 @foo() {
+$foo = comdat any
+define weak i32 @foo() comdat {
   ret i32 65
 }
 
 declare void @bar()
 
 define i32 @zed() {
   %1 = tail call i32 @foo()
   call void @bar()
   ret i32 %1
 }