linux-user: Add pidfd_open(), pidfd_send_signal() and pidfd_getfd() syscalls

I noticed those were missing when running the glib2.0 testsuite.
Add the syscalls including the strace output.

Signed-off-by: Helge Deller <deller@gmx.de>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20220918194555.83535-4-deller@gmx.de>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
3 files changed