lto: Fix streaming of loop->can_be_parallel [PR125717]

The can_be_parallel flag was not being streamed out, so any frontend
setting the flag (via annot_expr_parallel_kind) would not observe it doing
anything when LTO was enabled.

Bootstrapped and regtested on aarch64-linux-gnu.

Signed-off-by: Dhruv Chawla <dhruvc@nvidia.com>

gcc/ChangeLog:

	PR fortran/125717
	* lto-streamer-in.cc (input_cfg): Stream loop->can_be_parallel in.
	* lto-streamer-out.cc (output_cfg): Stream loop->can_be_parallel out.