{linux,bsd}-user: Pass pid to fork_end()

{linux,bsd}-user: Pass pid to fork_end()

The upcoming follow-fork-mode child support requires knowing the child
pid. Pass it down.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240219141628.246823-6-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240305121005.3528075-7-alex.bennee@linaro.org>