[clang] LLVM_FALLTHROUGH => [[fallthrough]]. NFC

Remove unneeded LLVM_FALLTHROUGH added after https://reviews.llvm.org/D131346

Author: MaskRay

clang/lib/CodeGen/CGBuiltin.cpp

@@ -3628,7 +3628,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     // frexpl instead of legalizing this type in the BE.
     if (&getTarget().getLongDoubleFormat() == &llvm::APFloat::PPCDoubleDouble())
       break;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   }
   case Builtin::BI__builtin_frexp:
   case Builtin::BI__builtin_frexpf:
@@ -5366,7 +5366,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
     case Builtin::BI__builtin_ptrauth_auth_and_resign:
       if (Args[4]->getType()->isPointerTy())
         Args[4] = Builder.CreatePtrToInt(Args[4], IntPtrTy);
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
 
     case Builtin::BI__builtin_ptrauth_auth:
     case Builtin::BI__builtin_ptrauth_sign_unauthenticated:
@@ -18850,7 +18850,7 @@ Value *CodeGenFunction::EmitAMDGPUBuiltinExpr(unsigned BuiltinID,
     case AMDGPU::BI__builtin_amdgcn_wmma_f16_16x16x16_f16_w32_gfx12:
     case AMDGPU::BI__builtin_amdgcn_wmma_f16_16x16x16_f16_w64_gfx12:
       AppendFalseForOpselArg = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AMDGPU::BI__builtin_amdgcn_wmma_f16_16x16x16_f16_w32:
     case AMDGPU::BI__builtin_amdgcn_wmma_f16_16x16x16_f16_w64:
       ArgsForMatchingMatrixTypes = {2, 0}; // CD, AB
@@ -18859,7 +18859,7 @@ Value *CodeGenFunction::EmitAMDGPUBuiltinExpr(unsigned BuiltinID,
     case AMDGPU::BI__builtin_amdgcn_wmma_bf16_16x16x16_bf16_w32_gfx12:
     case AMDGPU::BI__builtin_amdgcn_wmma_bf16_16x16x16_bf16_w64_gfx12:
       AppendFalseForOpselArg = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case AMDGPU::BI__builtin_amdgcn_wmma_bf16_16x16x16_bf16_w32:
     case AMDGPU::BI__builtin_amdgcn_wmma_bf16_16x16x16_bf16_w64:
       ArgsForMatchingMatrixTypes = {2, 0}; // CD, AB

clang/lib/CodeGen/CodeGenTypes.cpp

@@ -409,7 +409,7 @@ llvm::Type *CodeGenTypes::ConvertType(QualType T) {
       break;
     case BuiltinType::LongDouble:
       LongDoubleReferenced = true;
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case BuiltinType::BFloat16:
     case BuiltinType::Float:
     case BuiltinType::Double:

clang/lib/Parse/ParseOpenACC.cpp

@@ -327,7 +327,7 @@ OpenACCReductionOperator ParseReductionOperator(Parser &P) {
       return OpenACCReductionOperator::Max;
     if (ReductionKindTok.getIdentifierInfo()->isStr("min"))
       return OpenACCReductionOperator::Min;
-    LLVM_FALLTHROUGH;
+    [[fallthrough]];
   default:
     P.Diag(ReductionKindTok, diag::err_acc_invalid_reduction_operator);
     return OpenACCReductionOperator::Invalid;
@@ -945,7 +945,7 @@ Parser::OpenACCClauseParseResult Parser::ParseOpenACCClauseParams(
       // the 'update' clause, so we have to handle it here.  U se an assert to
       // make sure we get the right differentiator.
       assert(DirKind == OpenACCDirectiveKind::Update);
-      LLVM_FALLTHROUGH;
+      [[fallthrough]];
     case OpenACCClauseKind::Attach:
     case OpenACCClauseKind::Copy:
     case OpenACCClauseKind::Delete: