gccrs: Fix assignment operator overloads for AST and HIR patterns

gccrs: Fix assignment operator overloads for AST and HIR patterns

gcc/rust/ChangeLog:

	* ast/rust-pattern.h
	(StructPatternElements::operator=): Clear vector before inserting.
	(TupleStructItemsNoRange::operator=): Clear vector before inserting.
	(TupleStructItemsRange::operator=): Clear vectors before inserting.
	(TuplePatternItemsMultiple::operator=): Clear vector before inserting.
	(TuplePatternItemsRanged::operator=): Clear vectors before inserting.
	(SlicePattern::operator=): Clear vector before inserting.
	(AltPattern::operator=): Clear vector before inserting.
	* hir/tree/rust-hir-pattern.h
	(StructPatternElements::operator=): Clear vector before inserting.
	(TupleStructItemsNoRange::operator=): Clear vector before inserting.
	(TupleStructItemsRange::operator=): Clear vectors before inserting.
	(TuplePatternItemsMultiple::operator=): Clear vector before inserting.
	(TuplePatternItemsRanged::operator=): Clear vectors before inserting.
	(SlicePattern::operator=): Clear vector before inserting.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>