bitbake: bin/bitbake: add a check for /dev/shm existing

Python multiprocessing needs /dev/shm, and if it doesn't exist (e.g. in
a chroot environment) or is not writable, you'll get
"OSError: [Errno 38] Function not implemented" or
"OSError: [Errno 13] Permission denied" with a traceback, which doesn't
really help to explain what is wrong.

Implements [YOCTO #4407].

(Bitbake rev: e7460d01f281f913a94192e1f4bd20688164bdd4)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/bin/bitbake

@@ -43,6 +43,10 @@ from bb import server
 __version__ = "1.19.0"
 logger = logging.getLogger("BitBake")
 
+# Python multiprocessing requires /dev/shm
+if not os.access('/dev/shm', os.W_OK | os.X_OK):
+    sys.exit("FATAL: /dev/shm does not exist or is not writable")
+
 # Unbuffer stdout to avoid log truncation in the event
 # of an unorderly exit as well as to provide timely
 # updates to log files for use with tail