[flang] Attempt to silence new GCC warnings

[klausler]

Summary

Restructure three code sites that are now eliciting new warnings
from the latest GCC compiler. One of these looks like a
legitimate problem with a reference to an expression temporary.

Fixes https://github.com/llvm/llvm-project/issues/64200.

[clementval]

LGTM

[klausler]

Fix patch, it had a glitch in it that looks like an inadvertent editor paste.

[klausler]

Address warnings without breaking tests.

flang/lib/Lower/ConvertCall.cpp

public:
 
   bool argMayBeModifiedByCall(unsigned argIdx) const {
     assert(argIdx < caller.getPassedArguments().size() && "bad argument index");
     return caller.getPassedArguments()[argIdx].mayBeModifiedByCall();
   }
 
   bool canLoadActualArgumentBeforeLoop(unsigned argIdx) const {
     using PassBy = Fortran::lower::CallerInterface::PassEntityBy;
-    assert(argIdx < caller.getPassedArguments().size() && "bad argument index");
+    const auto &passedArgs{caller.getPassedArguments()};
+    assert(argIdx < passedArgs.size() && "bad argument index");
     // If the actual argument does not need to be passed via an address,
     // or will be passed in the address of a temporary copy, it can be loaded
     // before the elemental loop nest.
-    const auto &arg = caller.getPassedArguments()[argIdx];
+    const auto &arg{passedArgs[argIdx]};
     return arg.passBy == PassBy::Value ||
            arg.passBy == PassBy::BaseAddressValueAttribute;
   }
 
   mlir::Value computeDynamicCharacterResultLength(
       Fortran::lower::PreparedActualArguments &loweredActuals,
       CallContext &callContext) {
     TODO(callContext.loc,

flang/lib/Lower/OpenMP.cpp

 static bool
 checkForSymbolMatch(const Fortran::parser::AssignmentStmt &assignmentStmt) {
   // Check if the symbol on the LHS of the assignment statement is present in
   // the RHS expression
   const auto &var{std::get<Fortran::parser::Variable>(assignmentStmt.t)};
   const auto &expr{std::get<Fortran::parser::Expr>(assignmentStmt.t)};
   const auto *e{Fortran::semantics::GetExpr(expr)};
   const auto *v{Fortran::semantics::GetExpr(var)};
-  const Fortran::semantics::Symbol &varSymbol =
-      Fortran::evaluate::GetSymbolVector(*v).front();
+  auto varSyms{Fortran::evaluate::GetSymbolVector(*v)};
+  const Fortran::semantics::Symbol &varSymbol{*varSyms.front()};
   for (const Fortran::semantics::Symbol &symbol :
        Fortran::evaluate::GetSymbolVector(*e))
     if (varSymbol == symbol)
       return true;
   return false;
 }
 
 static void genOmpAtomicHintAndMemoryOrderClauses(

flang/lib/Semantics/runtime-type-info.cpp

 // Save an arbitrarily shaped array constant of some derived type
 // as an initialized data object in a scope.
 static SomeExpr SaveDerivedPointerTarget(Scope &scope, SourceName name,
     std::vector<evaluate::StructureConstructor> &&x,
     evaluate::ConstantSubscripts &&shape) {
   if (x.empty()) {
     return SomeExpr{evaluate::NullPointer{}};
   } else {
-    const auto &derivedType{x.front().GetType().GetDerivedTypeSpec()};
+    auto dyType{x.front().GetType()};
+    const auto &derivedType{dyType.GetDerivedTypeSpec()};
     ObjectEntityDetails object;
     DeclTypeSpec typeSpec{DeclTypeSpec::TypeDerived, derivedType};
     if (const DeclTypeSpec * spec{scope.FindType(typeSpec)}) {
       object.set_type(*spec);
     } else {
       object.set_type(scope.MakeDerivedType(
           DeclTypeSpec::TypeDerived, common::Clone(derivedType)));
     }