[MachineCombiner][AArch64] Change mayAlias to isLoadFoldBarrier

[jcohen-apple]

Missed commit from a recently cherry-picked branch

rdar://165133928

[jcohen-apple]

@swift-ci please test

[jcohen-apple]

@swift-ci please test llvm

[finagolfin]

I'm seeing something quite strange in trying to build the latest Nov. 20 trunk snapshot tag natively on Android AArch64:

ld.lld: error: undefined symbol: llvm::MachineInstr::dump() const
>>> referenced by AArch64InstrInfo.cpp
>>>               AArch64InstrInfo.cpp.o:(llvm::AArch64InstrInfo::getMachineCombinerPatterns(llvm::MachineInstr&, llvm::SmallVectorImpl<unsigned int>&, bool) const) in archive lib/libLLVMAArch64CodeGen.a

Applying this patch fixes it and I remembered that I had seen the same error before when building LLVM for a linux x86_64 host too.

Are the CI builds for the snapshot tags not necessarily built from that tagged commit but from nearby commits? I don't understand how the latest Nov. 20 trunk snapshot tag would have passed the linux CI otherwise.

@AnthonyLatsis, are there plans for another trunk snapshot tag soon, including this pull? Otherwise, anybody trying to build the Swift compiler with the Nov. 20 trunk snapshot tag during the upcoming weeklong break is likely to fail.