gccrs: Fix bad bounds checking for PartialOrd

gccrs: Fix bad bounds checking for PartialOrd

This was a nasty issue to debug, the issue was very eager type bounds
checking. So for example:

  pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs>

The super trait of PartialEq<Rhs> is a generic substitution and we reuse
our bounds code here for normal generic bounds and generics an invalid
bounds check was occuring when PartialEq<Rhs> was getting substituted becase
this is a trait doing proper bounds checking is not valid here because this
is telling us about the bounds in this case.

Fixes Rust-GCC#3836

gcc/rust/ChangeLog:

	* typecheck/rust-hir-trait-resolve.cc (TraitResolver::resolve_trait): track is super trait
	* typecheck/rust-hir-type-bounds.h: refactor bounds scan
	* typecheck/rust-hir-type-check-base.h: track from super trait
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): likewise
	* typecheck/rust-tyty-bounds.cc (TypeBoundsProbe::is_bound_satisfied_for_type): refactor
	(TypeBoundsProbe::scan): likewise
	(TypeBoundPredicate::apply_generic_arguments): likewise
	* typecheck/rust-tyty-subst.cc: optional bounds checking on parm subst
	* typecheck/rust-tyty-subst.h: likewise
	* typecheck/rust-tyty.h: likewise

gcc/testsuite/ChangeLog:

	* rust/compile/derive_partial_ord1.rs: this is now fully supported
	* rust/execute/torture/basic_partial_ord1.rs: add missing i32 impl
	* rust/execute/torture/basic_partial_ord2.rs: likewise
	* rust/compile/issue-3836.rs: New test.
	* rust/execute/torture/issue-3836.rs: New test.
	* rust/execute/torture/partial-ord-6.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>