gccrs: Refactor unify to hit a unify_site

gccrs: Refactor unify to hit a unify_site

This allows us to enforce better error handling on unify sites

gcc/rust/ChangeLog:

	* typecheck/rust-hir-type-check-base.cc (TypeCheckBase::unify_site): Add
	better unification function with debug calls.
	* typecheck/rust-autoderef.cc (AutoderefCycle::cycle): Add more debug
	calls and use new unify API.
	* typecheck/rust-coercion.cc (TypeCoercionRules::do_coercion): Likewise.
	(TypeCoercionRules::coerce_borrowed_pointer): Likewise.
	(TypeCoercionRules::select): Likewise.
	* typecheck/rust-hir-dot-operator.cc (MethodResolver::select): Likewise.
	* typecheck/rust-hir-trait-resolve.cc (TraitItemReference::resolve_item): Likewise.
	(TypeCheckBase::coercion_site): Likewise.
	(TypeCheckBase::cast_site): Likewise.
	* typecheck/rust-hir-type-check-base.h: Likewise.
	* typecheck/rust-hir-type-check-enumitem.cc (TypeCheckEnumItem::visit): Likewise.
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): Likewise.
	* typecheck/rust-hir-type-check-implitem.cc (TypeCheckTopLevelImplItem::visit): Likewise.
	(TypeCheckImplItem::visit): Likewise.
	* typecheck/rust-hir-type-check-item.cc (TypeCheckItem::visit): Likewise.
	* typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::resolve_segments): Likewise.
	* typecheck/rust-hir-type-check-pattern.cc (TypeCheckPattern::visit): Likewise.
	* typecheck/rust-hir-type-check-stmt.cc (TypeCheckStmt::visit): Likewise.
	* typecheck/rust-hir-type-check-struct.cc (TypeCheckStructExpr::resolve): Likewise.
	* typecheck/rust-hir-type-check-toplevel.cc (TypeCheckTopLevel::visit): Likewise.
	* typecheck/rust-hir-type-check-type.cc (TypeCheckType::visit): Likewise.
	* typecheck/rust-hir-type-check.cc (TypeResolution::Resolve): Likewise.
	* typecheck/rust-tyctx.cc (TypeCheckContext::peek_return_type): Likewise.
	* typecheck/rust-tyty-call.cc (TypeCheckMethodCallExpr::visit): Likewise.
	* typecheck/rust-tyty-cmp.h: Likewise.
	* typecheck/rust-tyty-rules.h: Likewise.
	* typecheck/rust-tyty.cc (BaseType::mappings_str): Likewise.
	(BaseType::debug): Print type name more clearly.
	(BaseType::debug_str): Add new function to print type pointer and name.
	(TupleType::get_name): Improve type name fetching function.
	(ReferenceType::get_name): Likewise.
	(PointerType::get_name): Likewise.
	* typecheck/rust-tyty.h: Refactor definitions outside of the header.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1152.rs: Fix dejagnu assertion.
	* rust/compile/tuple1.rs: Likewise.
	* rust/compile/type-alias1.rs: Likewise.
	* rust/execute/torture/operator_overload_9.rs: Likewise.
	* rust/execute/torture/slice1.rs: Rework test to use new parsing
	capability and stick to the original implementation.