regen-mncc-py.sh: Document how to obtain required bins from source

Change-Id: Ifc54ea883dd9f11bf6497e81eaa00bb6ddf50807

regen-mncc-py.sh

@@ -3,14 +3,36 @@ echo This script requires that python-ctypeslib is installed on the system
 echo Unfortunately, this package is long unmaintained and only available on Debian8
 echo
 
+# If your distro doesn't provide python-ctypeslib:
+# svn co "https://svn.python.org/projects/ctypes/trunk/ctypeslib/"
+# cd ctypeslib
+# python2 ./setup.py install --prefix /tmp/out
+# ln -s h2xml.py /tmp/out/bin/h2xml
+# ln -s xml2py.py /tmp/out/bin/xml2py
+# export PYTHONPATH="$PYTHONPATH:/tmp/out/lib/python2.7/site-packages"
+# export PATH="$PATH:/tmp/out/bin/"
+# ./regen-mncc-py.sh
+# == Troubleshooting:
+# * h2ml: Failing with tracebak OSError Not found:
+#   One may be missing gccxml. On arch, install gccxml-git from AUR.
+# * h2xml failing due to missing gccxml_builtins.h:
+#   Create empty file /tmp/include/gccxml_builtins.h and pass "-I /tmp/include/" to h2xml.
+# * Missing __builtin_bswap16/32/64:
+#   Copy from /usr/include/bits/byteswap.h defines __bswap_constant_16/32/64 to
+#   either start of mncc.h itself or /tmp/include/gccxml_builtins.h, and rename
+#   them as __builtin_bswap16/32/64.
+
 if [ ! -x `which h2xml` ]; then
 	echo No h2xml executable found - python-ctypeslib not installed?
+	exit 1
 fi
 
 if [ ! -x `which xml2py` ]; then
 	echo No xml2py executable found - python-ctypeslib not installed?
+	exit 1
 fi
 
+set -xe
 cp ./mncc.h /tmp/mncc.h
-h2xml ./mncc.h -c -o mncc.xml
+h2xml -I /tmp/include/ ./mncc.h -c -o mncc.xml
 xml2py mncc.xml -k dest -v -o mncc.py