self-hosted riscv backend missing features

[andrewrk]

zig/src/target.zig

Lines 587 to 610 in 7185cca

	.error_return_trace => switch (backend) {
	.stage2_llvm => true,
	else => false,
	},
	.is_named_enum_value => switch (backend) {
	.stage2_llvm => true,
	else => false,
	},
	.error_set_has_value => switch (backend) {
	.stage2_llvm, .stage2_wasm => true,
	else => false,
	},
	.field_reordering => switch (backend) {
	.stage2_c, .stage2_llvm => true,
	else => false,
	},
	.safety_checked_instructions => switch (backend) {
	.stage2_llvm => true,
	else => false,
	},
	.separate_thread => switch (backend) {
	.stage2_llvm => false,
	else => true,
	},

This issue can be closed when all the compiler features are enabled for the riscv backend.