gccrs: Fix handling of constants in paths

Fixes Rust-GCC/gccrs#4851

gcc/rust/ChangeLog:

	* backend/rust-compile-pattern.cc (CompilePatternCheckExpr::visit): handle non ADT
	* typecheck/rust-hir-type-check-pattern.cc (TypeCheckPattern::visit): likewise

gcc/testsuite/ChangeLog:

	* rust/compile/issue-4851.rs: New test.

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