[Sema] Remove an unnecessary cast (NFC) (#146622)

Since both alignment and Alignment are of the same type, this patch
renames alignment to Alignment while removing the cast statement.

Author: kazutakahirata

clang/lib/Sema/SemaAttr.cpp

@@ -436,7 +436,7 @@ void Sema::ActOnPragmaClangSection(SourceLocation PragmaLoc,
 }
 
 void Sema::ActOnPragmaPack(SourceLocation PragmaLoc, PragmaMsStackAction Action,
-                           StringRef SlotLabel, Expr *alignment) {
+                           StringRef SlotLabel, Expr *Alignment) {
   bool IsXLPragma = getLangOpts().XLPragmaPack;
   // XL pragma pack does not support identifier syntax.
   if (IsXLPragma && !SlotLabel.empty()) {
@@ -445,7 +445,6 @@ void Sema::ActOnPragmaPack(SourceLocation PragmaLoc, PragmaMsStackAction Action,
   }
 
   const AlignPackInfo CurVal = AlignPackStack.CurrentValue;
-  Expr *Alignment = static_cast<Expr *>(alignment);
 
   // If specified then alignment must be a "small" power of two.
   unsigned AlignmentVal = 0;