[Libomptarget] Replace Value RAII with default value

[jhuber6]

Summary

This patch replaces the ValueRAII pointer with a default 'nullptr'
value. Previously this was initialized as a reference to an existing
variable. The use of this variable caused overhead as the compiler could
not look through the uses and determine that it was unused if 'Active'
was not set. Because of this accesses to the variable would be left in
the runtime once compiled.

Fixes #53641

[jdoerfert]

LG

openmp/libomptarget/DeviceRTL/include/State.h

142

Val is not used anymore, delete it.

[jdoerfert]

openmp/libomptarget/DeviceRTL/include/State.h

142

My bad, it is used.

openmp/libomptarget/DeviceRTL/include/State.h

Ty &set(Ty UpdateVal) {
     return (lookup(/* IsReadonly */ false, /* IdentTy */ nullptr) = UpdateVal);
   }
 
   template <typename VTy, typename Ty2> friend struct ValueRAII;
 };
 
 template <typename VTy, typename Ty> struct ValueRAII {
   ValueRAII(VTy &V, Ty NewValue, Ty OldValue, bool Active, IdentTy *Ident)
-      : Ptr(Active ? V.lookup(/* IsReadonly */ false, Ident) : Val),
+      : Ptr(Active ? &V.lookup(/* IsReadonly */ false, Ident) : nullptr),
         Val(OldValue), Active(Active) {
     if (!Active)
       return;
-    ASSERT(Ptr == OldValue && "ValueRAII initialization with wrong old value!");
-    Ptr = NewValue;
+    ASSERT(*Ptr == OldValue &&
+           "ValueRAII initialization with wrong old value!");
+    *Ptr = NewValue;
   }
   ~ValueRAII() {
     if (Active)
-      Ptr = Val;
+      *Ptr = Val;
   }
 
 private:
-  Ty &Ptr;
+  Ty *Ptr;
   Ty Val;
   bool Active;
 };
 
 /// TODO
 inline state::Value<uint32_t, state::VK_RunSchedChunk> RunSchedChunk;
 
 /// TODO
 inline state::Value<uint32_t, state::VK_ParallelTeamSize> ParallelTeamSize;