[Alignment][NFC] Convert AllocaInst to MaybeAlign

Summary:
This is patch is part of a series to introduce an Alignment type.
See this thread for context: http://lists.llvm.org/pipermail/llvm-dev/2019-July/133851.html
See this patch for the introduction of the type: https://reviews.llvm.org/D64790

Reviewers: courbet

Reviewed By: courbet

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69301

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -4761,7 +4761,7 @@ Error BitcodeReader::parseFunctionBody(Function *F) {
       const DataLayout &DL = TheModule->getDataLayout();
       unsigned AS = DL.getAllocaAddrSpace();
 
-      AllocaInst *AI = new AllocaInst(Ty, AS, Size, Align ? Align->value() : 0);
+      AllocaInst *AI = new AllocaInst(Ty, AS, Size, Align);
       AI->setUsedWithInAlloca(InAlloca);
       AI->setSwiftError(SwiftError);
       I = AI;