mGCA: Support directly represented negated literals

[khyperia]

fixes #152123

PatExprKind already awkwardly tacks on a negated: bool for the same purpose:

rust/compiler/rustc_hir/src/hir.rs

Lines 1954 to 1959 in 8bccf12

	Lit {
	lit: Lit,
	// FIXME: move this into `Lit` and handle negated literal expressions
	// once instead of matching on unop neg expressions everywhere.
	negated: bool,
	},

perhaps one day we should indeed do that FIXME...

r? @BoxyUwU