ipa-fnsummary: Remove inconsistent bp_pack_value

ipa-fnsummary: Remove inconsistent bp_pack_value

There is one inconsistent bit-field streaming out and in.
On the side of streaming in:

    bp_pack_value (&bp, info->inlinable, 1);
    bp_pack_value (&bp, false, 1);
    bp_pack_value (&bp, info->fp_expressions, 1);

while on the side of the streaming out:

    info->inlinable = bp_unpack_value (&bp, 1);
    info->fp_expressions = bp_unpack_value (&bp, 1)

The removal of Cilk Plus support r8-4956 missed to remove
the streaming out of the bit, instead just change the value
for streaming out to be always false.

By hacking fp_expression_p to always return true, I can see
it reads the wrong fp_expressions value (false) out in wpa.

GCC12 adopts commit 63c6446f77b9001d26f973114450d790749f282b
which removes the inconsistent streaming out instead.

gcc/ChangeLog:

	* ipa-fnsummary.c (inline_read_section): Unpack a dummy bit
	to keep consistent with the side of streaming out.