Update Dockerfiles and CI scripts to Ubuntu 20.04 and simplify them.

libyul/backends/evm/EVMCodeTransform.cpp

@@ -85,11 +85,11 @@ void VariableReferenceCounter::operator()(Block const& _block)
 void VariableReferenceCounter::increaseRefIfFound(YulString _variableName)
 {
 	m_scope->lookup(_variableName, GenericVisitor{
-		[=](Scope::Variable const& _var)
+		[&](Scope::Variable const& _var)
 		{
 			++m_context.variableReferences[&_var];
 		},
-		[=](Scope::Function const&) { }
+		[](Scope::Function const&) { }
 	});
 }
 
@@ -272,7 +272,7 @@ void CodeTransform::operator()(FunctionCall const& _call)
 
 		Scope::Function* function = nullptr;
 		yulAssert(m_scope->lookup(_call.functionName.name, GenericVisitor{
-			[=](Scope::Variable&) { yulAssert(false, "Expected function name."); },
+			[](Scope::Variable&) { yulAssert(false, "Expected function name."); },
 			[&](Scope::Function& _function) { function = &_function; }
 		}), "Function name not found.");
 		yulAssert(function, "");
@@ -296,7 +296,7 @@ void CodeTransform::operator()(Identifier const& _identifier)
 	// First search internals, then externals.
 	yulAssert(m_scope, "");
 	if (m_scope->lookup(_identifier.name, GenericVisitor{
-		[=](Scope::Variable& _var)
+		[&](Scope::Variable& _var)
 		{
 			// TODO: opportunity for optimization: Do not DUP if this is the last reference
 			// to the top most element of the stack
@@ -307,7 +307,7 @@ void CodeTransform::operator()(Identifier const& _identifier)
 				m_assembly.appendConstant(u256(0));
 			decreaseReference(_identifier.name, _var);
 		},
-		[=](Scope::Function&)
+		[](Scope::Function&)
 		{
 			yulAssert(false, "Function not removed during desugaring.");
 		}