Remove the 's' DataLayout specification

During the years there have been some attempts at figuring out how to
align byval arguments. A look at the commit log suggests that they
were

* Use the ABI alignment.
* When that was not sufficient for x86-64, I added the 's' specification to
  DataLayout.
* When that was not sufficient Evan added the virtual getByValTypeAlignment.
* When even that was not sufficient, we just got the FE to add the alignment
  to the byval.

This patch is just a simple cleanup that removes my first attempt at fixing the
problem. I also added an AArch64 implementation of getByValTypeAlignment to
make sure this patch is a nop. I also left the 's' parsing for backward
compatibility.

I will send a short email to llvmdev about the change for anyone maintaining
an out of tree target.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198287 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/TargetLoweringBase.cpp

@@ -1285,7 +1285,7 @@ void llvm::GetReturnInfo(Type* ReturnType, AttributeSet attr,
 /// function arguments in the caller parameter area.  This is the actual
 /// alignment, not its logarithm.
 unsigned TargetLoweringBase::getByValTypeAlignment(Type *Ty) const {
-  return TD->getCallFrameTypeAlignment(Ty);
+  return TD->getABITypeAlignment(Ty);
 }
 
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