[flang] Making Scope::FindCommonBlock a const member

[Renaud-K]

Summary

Making Scope::FindCommonBlock a const member

[Renaud-K]

reated a full diff with "git show HEAD -U999999" instead of just "git show HEAD"

[klausler]

Looks okay to me.

[PeteSteinfeld]

All builds, tests, and looks good.

flang/include/flang/Semantics/scope.h

public:
   }
   void add_equivalenceSet(EquivalenceSet &&);
   // Cray pointers are saved as map of pointee name -> pointer symbol
   const mapType &crayPointers() const { return crayPointers_; }
   void add_crayPointer(const SourceName &, Symbol &);
   mapType &commonBlocks() { return commonBlocks_; }
   const mapType &commonBlocks() const { return commonBlocks_; }
   Symbol &MakeCommonBlock(const SourceName &);
-  Symbol *FindCommonBlock(const SourceName &);
+  Symbol *FindCommonBlock(const SourceName &) const;
 
   /// Make a Symbol but don't add it to the scope.
   template <typename D>
   common::IfNoLvalue<Symbol &, D> MakeSymbol(
       const SourceName &name, Attrs attrs, D &&details) {
     return allSymbols.Make(*this, name, attrs, std::move(details));
   }
 

flang/lib/Semantics/scope.cpp

Symbol &Scope::MakeCommonBlock(const SourceName &name) {
   if (it != commonBlocks_.end()) {
     return *it->second;
   } else {
     Symbol &symbol{MakeSymbol(name, Attrs{}, CommonBlockDetails{})};
     commonBlocks_.emplace(name, symbol);
     return symbol;
   }
 }
-Symbol *Scope::FindCommonBlock(const SourceName &name) {
+Symbol *Scope::FindCommonBlock(const SourceName &name) const {
   const auto it{commonBlocks_.find(name)};
   return it != commonBlocks_.end() ? &*it->second : nullptr;
 }
 
 Scope *Scope::FindSubmodule(const SourceName &name) const {
   auto it{submodules_.find(name)};
   if (it == submodules_.end()) {
     return nullptr;