[ASAN] NFC: Remove redundant variable

`StackAlignment` has only one use: `StackAlignment = std::max(StackAlignment, AI.getAlignment());` So it is redundant.

Reviewed By: vitalybuka, MTC

Differential Revision: https://reviews.llvm.org/D106741

Author: Enna1

llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp

@@ -932,7 +932,6 @@ struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
   SmallVector<AllocaInst *, 16> AllocaVec;
   SmallVector<AllocaInst *, 16> StaticAllocasToMoveUp;
   SmallVector<Instruction *, 8> RetVec;
-  unsigned StackAlignment;
 
   FunctionCallee AsanStackMallocFunc[kMaxAsanStackMallocSizeClass + 1],
       AsanStackFreeFunc[kMaxAsanStackMallocSizeClass + 1];
@@ -964,7 +963,6 @@ struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
       : F(F), ASan(ASan), DIB(*F.getParent(), /*AllowUnresolved*/ false),
         C(ASan.C), IntptrTy(ASan.IntptrTy),
         IntptrPtrTy(PointerType::get(IntptrTy, 0)), Mapping(ASan.Mapping),
-        StackAlignment(1 << Mapping.Scale),
         PoisonStack(ClStack &&
                     !Triple(F.getParent()->getTargetTriple()).isAMDGPU()) {}
 
@@ -1088,7 +1086,6 @@ struct FunctionStackPoisoner : public InstVisitor<FunctionStackPoisoner> {
       return;
     }
 
-    StackAlignment = std::max(StackAlignment, AI.getAlignment());
     if (!AI.isStaticAlloca())
       DynamicAllocaVec.push_back(&AI);
     else