[flang] Attempt to silence new GCC warnings

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.

Differential Revision: https://reviews.llvm.org/D156750

flang/lib/Lower/ConvertCall.cpp

@@ -1693,11 +1693,12 @@ public:
 
   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;
   }

flang/lib/Lower/OpenMP.cpp

@@ -2662,8 +2662,8 @@ checkForSymbolMatch(const Fortran::parser::AssignmentStmt &assignmentStmt) {
   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)

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

@@ -202,7 +202,8 @@ static SomeExpr SaveDerivedPointerTarget(Scope &scope, SourceName name,
   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)}) {