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>

scripts/jobserver-exec

@@ -26,11 +26,20 @@ try:
 	# If the MAKEFLAGS variable contains multiple instances of the
 	# --jobserver-auth= option, the last one is relevant.
 	fds = opts[-1].split("=", 1)[1]
-	reader, writer = [int(x) for x in fds.split(",", 1)]
-	# Open a private copy of reader to avoid setting nonblocking
-	# on an unexpecting process with the same reader fd.
-	reader = os.open("/proc/self/fd/%d" % (reader),
-			 os.O_RDONLY | os.O_NONBLOCK)
+
+	# Starting with GNU Make 4.4, named pipes are used for reader and writer.
+	# Example argument: --jobserver-auth=fifo:/tmp/GMfifo8134
+	_, _, path = fds.partition('fifo:')
+
+	if path:
+		reader = os.open(path, os.O_RDONLY | os.O_NONBLOCK)
+		writer = os.open(path, os.O_WRONLY)
+	else:
+		reader, writer = [int(x) for x in fds.split(",", 1)]
+		# Open a private copy of reader to avoid setting nonblocking
+		# on an unexpecting process with the same reader fd.
+		reader = os.open("/proc/self/fd/%d" % (reader),
+				 os.O_RDONLY | os.O_NONBLOCK)
 
 	# Read out as many jobserver slots as possible.
 	while True: