[Alignment][NFC] Mark IRTranslator::getMemOpAlignment deprecated

[gchatelet]

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

[arsenm]

llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h

585–589

The number of uses in GlobalISel is so small, there's no reason to bother with this. It should be trivial to eliminate the old forms

[gchatelet]

llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h

585–589

Are you sure it's not used by out of tree users?
If so, I'm happy to drop it.

My plan is to start removing LLVM_ATTRIBUTE_DEPRECATED functions that have been introduced in the last release.

llvm/include/llvm/CodeGen/GlobalISel/IRTranslator.h

private:
 
   /// Get the frame index that represents \p Val.
   /// If such VReg does not exist, it is created.
   int getOrCreateFrameIndex(const AllocaInst &AI);
 
   /// Get the alignment of the given memory operation instruction. This will
   /// either be the explicitly specified value or the ABI-required alignment for
   /// the type being accessed (according to the Module's DataLayout).
-  /// FIXME: Remove once transition to Align is over.
-  inline unsigned getMemOpAlignment(const Instruction &I) {
+  LLVM_ATTRIBUTE_DEPRECATED(
+      inline unsigned getMemOpAlignment(const Instruction &I),
+      "Use getMemOpAlign instead") {
     return getMemOpAlign(I).value();
   }
 
   /// Get the alignment of the given memory operation instruction. This will
   /// either be the explicitly specified value or the ABI-required alignment for
   /// the type being accessed (according to the Module's DataLayout).
   Align getMemOpAlign(const Instruction &I);
 
   /// Get the MachineBasicBlock that represents \p BB. Specifically, the block
   /// returned will be the head of the translated block (suitable for branch