[flang][OpenMP] Reintroduce TODO for FIR lowering of linear clause (#144883)

Current design of the linear clause lowering and translation shifts all
responsibility for handling the clause (like privatisation, linear
stepping, finalisation, and emission of synchronisation barriers) to the
IRBuilder. However in certain corner cases (like associated loops in or
before OpenMP version 4.5), variables are are implicitly linear. This
currently causes a problem with the existing linear clause
implementation. Hence, re-introduce TODO on the linear clause until the
linear clause lowering/translation are robust enough to handle such
cases as well.

Fixes #142935

Author: NimishMishra

flang/lib/Lower/OpenMP/OpenMP.cpp

@@ -1968,13 +1968,13 @@ static void genWsloopClauses(
     llvm::SmallVectorImpl<const semantics::Symbol *> &reductionSyms) {
   ClauseProcessor cp(converter, semaCtx, clauses);
   cp.processNowait(clauseOps);
-  cp.processLinear(clauseOps);
   cp.processOrder(clauseOps);
   cp.processOrdered(clauseOps);
   cp.processReduction(loc, clauseOps, reductionSyms);
   cp.processSchedule(stmtCtx, clauseOps);
 
-  cp.processTODO<clause::Allocate>(loc, llvm::omp::Directive::OMPD_do);
+  cp.processTODO<clause::Allocate, clause::Linear>(
+      loc, llvm::omp::Directive::OMPD_do);
 }
 
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