scripts: support GNU make 4.4 in jobserver-exec

Starting with GNU make 4.4, --jobserver-auth newly uses named
pipe (fifo) instead of part of opened file descriptors:
https://www.gnu.org/software/make/manual/html_node/POSIX-Jobserver.html



Support also the new format.

Signed-off-by: Martin Liska <mliska@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>