Determine the running kernel and it's config on the Raspberry Pi target machine.

uname -a
Linux pi3 3.12.28+ #709 PREEMPT Mon Sep 8 15:28:00 BST 2014 armv6l GNU/Linux
zgrep "* firmware as of" /usr/share/doc/raspberrypi-bootloader/changelog.Debian.gz | head -1 | awk '{ print $5 }'
53d1ae311226b5c
zcat /proc/config.gz > 53d1ae311226b5c.config

Examples.

Linux pi3 3.6.11+ #538 PREEMPT Fri Aug 30 20:42:08 BST 2013 armv6l GNU/Linux  d4f5315cfac4e
Linux pi3 3.10.23+ #608 PREEMPT Mon Dec 9 21:11:23 GMT 2013 armv6l GNU/Linux  9d34d0475f9
Linux pi3 3.10.24+ #614 PREEMPT Thu Dec 19 20:38:42 GMT 2013 armv6l GNU/Linux c32bc633039cd9
Linux pi3 3.10.25+ #622 PREEMPT Fri Jan 3 18:41:00 GMT 2014 armv6l GNU/Linux  030082b403b
Linux pi3 3.12.28+ #709 PREEMPT Mon Sep 8 15:28:00 BST 2014 armv6l GNU/Linux  53d1ae311226b5c

Determine the kernel hash for the firmware.

wget -q https://raw.github.com/raspberrypi/firmware/53d1ae311226b5c/extra/git_hash -O /tmp/hash
cat /tmp/hash 
94a382fed1a5ec303eef9e1f3439df8f759ba60c

Examples.

3.6.11+  d4f5315cfac4e   1587f775d0a3c437485262ba951afc5e30be69fa
3.10.23+ 9d34d0475f9     c15430e6a01e1332032d83f6484a866504e8ee97
3.10.24+ c32bc633039cd9  4bbea92eae6c0792e85a4ba079d367ac6aa77fb5
3.10.25+ 030082b403b     16eb921a96db3dc3555a65b53b99c15753e6b770
3.12.28+ 53d1ae311226b5c 94a382fed1a5ec303eef9e1f3439df8f759ba60c

On the build host fetch the raspberry pi build tools.

mkdir -p /embedded/rpi
cd /embedded/rpi
git clone git://github.com/raspberrypi/tools.git

Fetch the kernel source for the previously determined hash.

rm -Rf /embedded/rpi/linux
cd /embedded/rpi
git clone https://github.com/raspberrypi/linux.git
cd /embedded/rpi/linux/
git checkout 94a382fed1a5ec303eef9e1f3439df8f759ba60c
git reset --hard

Prepare to build kernel and copy over configuration.

make ARCH=arm mrproper
scp pi@pi:53d1ae311226b5c.config .config

Build the kernel using the raspberry pi build tools.

make ARCH=arm oldconfig
make ARCH=arm CROSS_COMPILE=/embedded/rpi/tools/arm-bcm2708/arm-bcm2708hardfp-linux-gnueabi/bin/arm-bcm2708hardfp-linux-gnueabi- -j 8

Build the GPIO bit-bang module and copy to target machine.

hg clone http://hg.kewl.org/pub/gpio-bb
cd gpio-bb/rpi-raspbian
make 
scp ../module/src/gpio-bb.ko pi@pi:

Install the module on the Raspberry Pi target machine (Eg. 3.12.28+).

mkdir -p /lib/modules/3.12.28+/kernel/local/
cp gpio-bb.ko /lib/modules/3.12.28+/kernel/local/
chown -R 0:0 /lib/modules/3.12.28+/kernel/local/
depmod -a

Load modules on target machine.

/etc/modprobe.d/modprobe.conf:
install gpio-bb modprobe --ignore-install gpio-bb && modprobe gpio-bb && mknod /dev/gpio-bb c 180 0

modprobe gpio-bb