gccrs: Rework function special parameters

Make self param and variadic param Param, introduce Param class and make
function parameters param too.
Self can now be represented as a standard parameter and is thus no longer
required as a separate function attribute.
Prevent self pointers and allow self in standard functions during parsing
so they could be rejected at a later stage.

gcc/rust/ChangeLog:

	* ast/rust-ast-collector.cc (TokenCollector::visit): Add visitor for
	VariadicParam and remove Self parameter visitor from Function visit.
	* expand/rust-cfg-strip.cc (CfgStrip::maybe_strip_self_param): Remove
	function.
	(CfgStrip::maybe_strip_trait_method_decl): Remove self parameter visit.
	(CfgStrip::maybe_strip_function_params): Handle new function
	parameters.
	(CfgStrip::visit): Handle VariadicParam, SelfParam and FunctionParam.
	* expand/rust-expand-visitor.cc (ExpandVisitor::expand_self_param):
	Remove function.
	(ExpandVisitor::expand_trait_method_decl): Do not visit self parameter.
	(ExpandVisitor::visit): Add visit for VariadicParam, FunctionParam and
	SelfParam.
	(ExpandVisitor::expand_function_params): Visit parameters instead.
	* expand/rust-expand-visitor.h: Update function prototypes.
	* resolve/rust-ast-resolve-item.cc (ResolveItem::visit): Update visit
	with new parameters.
	(ResolveTraitItems::visit): Likewise.
	* resolve/rust-early-name-resolver.cc (EarlyNameResolver::visit):
	Update visit functions with the new visitor functions for VariadicParam
	SelfParam and FunctionParam.
	* resolve/rust-early-name-resolver.h: Update function prototypes.
	* ast/rust-ast-visitor.cc (DefaultASTVisitor::visit): Update visitor
	according to the new function parameter structures.
	* ast/rust-ast-visitor.h: Update prototypes and add visitor virtual
	functions for SelfParam, FunctionParam and VariadicParam.
	* ast/rust-ast.cc (Function::Function): Move constructor in
	implementation instead of header.
	(Function::operator=): Likewise.
	(Function::as_string): Update function with pointer dereference.
	(VariadicParam::as_string): Likewise.
	(TraitFunctionDecl::as_string): Likewise.
	(TraitMethodDecl::as_string): Likewise.
	(FunctionParam::accept_vis): Add function for visitor.
	(SelfParam::accept_vis): Likewise.
	(VariadicParam::accept_vis): Likewise.
	(TraitItemFunc::TraitItemFunc): Move constructor to implementation
	file.
	(TraitItemFunc::operator=): Likewise.
	(TraitItemMethod::TraitItemMethod): Likewise.
	(TraitItemMethod::operator=): Likewise.
	* ast/rust-item.h (class Function): Remove self optional member.
	(class TraitMethodDecl): Likewise.
	(class TraitFunctionDecl): Likewise.
	(class Param): Add abstract parameter class.
	(class SelfParam): Inherit from Param and remove parameter common
	members.
	(class FunctionParam): Likewise.
	(class VariadicParam): Likewise.
	(struct Visibility): Move structure declaration.
	(class VisItem):  Likewise.
	* checks/errors/rust-ast-validation.cc (ASTValidation::visit): Add
	a self parameter check during AST validation.
	* checks/errors/rust-ast-validation.h: Add function prototype.
	* expand/rust-derive-clone.cc (DeriveClone::clone_fn): Update function
	constructor.
	* hir/rust-ast-lower-base.cc (ASTLoweringBase::lower_self): Rework
	function for the new parameters.
	(ASTLoweringBase::visit): Add visit functions for VariadicParam,
	FunctionParam and SelfParam.
	* hir/rust-ast-lower-base.h: Update function prototypes.
	* parse/rust-parse-impl.h (Parser::parse_function): Update function
	according to new function representation.
	(Parser::parse_function_param): Return vector of abstract param instead
	of FunctionParam.
	(Parser::parse_method): Update according to new representation.
	(Parser::parse_trait_item): Likewise.
	(Parser::parse_self_param): Error out with
	self pointers and prevent the lexer from eating regular function
	parameters. Update return type.
	* parse/rust-parse.h: Update function return types.
	* ast/rust-ast-collector.h: Add VariadicParam visit prototype.
	* ast/rust-ast.h (struct Visibility): Move struct declaration.
	(class VisItem): Likewise.
	* ast/rust-expr.h: Update included files.
	* checks/errors/rust-feature-gate.h: Add visitor functions for
	SelfParam, FunctionParam and VariadicParam.
	* expand/rust-cfg-strip.h: Update function prototypes.
	* expand/rust-derive.h: Likewise.
	* hir/rust-ast-lower-implitem.h: Handle special arguments.
	* hir/rust-ast-lower-item.cc (ASTLoweringItem::visit): Likewise.
	* metadata/rust-export-metadata.cc (ExportContext::emit_function):
	Likewise.
	* resolve/rust-ast-resolve-base.cc (ResolverBase::visit): Add visitor
	functions.
	* resolve/rust-ast-resolve-base.h: Update prototypes.
	* resolve/rust-ast-resolve-stmt.h: Handle new parameter kind.
	* resolve/rust-default-resolver.cc (DefaultResolver::visit): Likewise.
	* resolve/rust-default-resolver.h: Update prototype.
	* util/rust-attributes.cc (AttributeChecker::visit): Add visitor
	functions for SelfParam and VariadicParam.
	* util/rust-attributes.h: Add visit prototypes.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>