ASan: Use `createSanitizerCtor` to create ctor, and call `__asan_init`

[ismailp]

Updated after changes in D8777;

• createSanitizerCtor renamed to createSanitizerCtorAndInitFunctions to match with changes in D8777
• Added simple check to ensure ASan's ctor is added to module ctors, and __asan_init_v5 is called from ctor

[samsonov]

LGTM

lib/Transforms/Instrumentation/AddressSanitizer.cpp

bool AddressSanitizer::doInitialization(Module &M) {
 
   GlobalsMD.init(M);
 
   C = &(M.getContext());
   LongSize = M.getDataLayout().getPointerSizeInBits();
   IntptrTy = Type::getIntNTy(*C, LongSize);
   TargetTriple = Triple(M.getTargetTriple());
 
-  AsanCtorFunction =
-      Function::Create(FunctionType::get(Type::getVoidTy(*C), false),
-                       GlobalValue::InternalLinkage, kAsanModuleCtorName, &M);
-  BasicBlock *AsanCtorBB = BasicBlock::Create(*C, "", AsanCtorFunction);
-  // call __asan_init in the module ctor.
-  IRBuilder<> IRB(ReturnInst::Create(*C, AsanCtorBB));
-  AsanInitFunction = checkInterfaceFunction(
-      M.getOrInsertFunction(kAsanInitName, IRB.getVoidTy(), nullptr));
-  AsanInitFunction->setLinkage(Function::ExternalLinkage);
-  IRB.CreateCall(AsanInitFunction);
+  AsanCtorFunction = createSanitizerCtor(M, kAsanModuleCtorName, kAsanInitName,
+                                         &AsanInitFunction);
 
   Mapping = getShadowMapping(TargetTriple, LongSize);
 
   appendToGlobalCtors(M, AsanCtorFunction, kAsanCtorAndDtorPriority);
   return true;
 }
 
 bool AddressSanitizer::maybeInsertAsanInitAtFunctionEntry(Function &F) {