gccrs: fix parser error on parenthesis types

gccrs: fix parser error on parenthesis types

Do not cast parenthesised types to TraitBound types.

Fixes Rust-GCC#4148

gcc/rust/ChangeLog:

	* ast/rust-path.cc (TypePath::to_trait_bound): Check if in
	parenthesis.
	* hir/tree/rust-hir-type.cc (ParenthesisedType::to_trait_bound):
	Likewise.
	* hir/tree/rust-hir.cc (TypePath::to_trait_bound): Likewise.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-4148.rs: Test should produce errors.

Signed-off-by: lenny.chiadmi-delage <lenny.chiadmi-delage@epita.fr>