What are we doing here?

As far as I understand the problem, there are two worlds:
Raspberry Pi Foundation on the one hand, the OpenWRT Team on the other one.
OpenWRT does try to patch "Default Kernels" until they work out with the intended Plattform, which does work in most cases very well.
The problem is, RPi is an new target for the latest OpenWRT Release - and does work - but it does not get much love of the devs:
No trunk compiles or nightlys of the Image or the packages - i.e.
And - the "so patched Kernel" does not represent the state of the art of the RPi Kernel Development at all:
I got many errors of the "first days of Pi", like the loved "SDcard error" which corrupted the whole filesystem and such.

User arsiskk of the raspberrypi-openwrt project had the same problem.
The rpi-openwrt project tried to deliever the first OpenWRT Experience to the RPi Users - competing with OpenWRT - and succeeded.
But the problem somehow remained: The old kernel was lingering there and the Team seemed to have given up the project after RPi
became an official target (https://code.google.com/p/raspberrypi-openwrt/).
So arsiskk developed a procedure to compile the raspberrypi-openwrt Code with the latest RPi Kernel - which worked awesome.
But as the project seems to be quite dead now - I tried to convert his idea and use it on the offical OpenWRT Trunk Sourcetree.
And that worked.

So long story short, what are we doing here?
We grab the trunk OpenWRT official source code, load the offical RPi Kernel into it, delete a bunch of files
which would only be needed to supply an standard kernel with a bit of RPi support and compile it.
In the end we will have the latest OpenWRT trunk with the latest RPi Kernel.
The only problem: You would sometimes need to rebuild packages which do not work with the official, but old (3.6.11, compared to OpenWRTs 3.10.4) Kernel.
And - you can't update the OpenWRT trunk that easily.
It is basically an "build and throw away" system.
But it works!
# Dependencies needed
sudo apt-get install build-essential subversion git-core libncurses5-dev zlib1g-dev gawk flex quilt libssl-dev xsltproc libxml-parser-perl mercurial bzr ecj cvs unzip

# Prepare Enviroment (Trunk)
cd ~
mkdir rpi_openwrt
cd rpi_openwrt
git clone git://git.openwrt.org/openwrt.git
cd openwrt
mkdir dl
# Install Packages
./scripts/feeds update -a
./scripts/feeds install -a

# Check Enviroment
make defconfig
make prereq

# Download Kernel and Prepare:
cd /tmp
wget https://github.com/raspberrypi/linux/archive/rpi-3.6.y.tar.gz
tar xfvz rpi-3.6.y.tar.gz
mv linux-rpi-3.6.y linux-3.6.11
tar cvf - linux-3.6.11/ | lzma > linux-3.6.11.tar.xz
mv linux-3.6.11.tar.xz ~/rpi_openwrt/openwrt/dl/

# Prepare Target
cd ~/rpi_openwrt/openwrt/target/linux/brcm2708/
vi Makefile
change LINUX_VERSION to LINUX_VERSION:=3.6.11
mkdir patches-3.6
cp config-3.10 config-3.6
cd ../generic/
cd patches-3.6
#if not exists, dl latest official openwrt, copy files from openwrt/target/linux/generic/patches-3.6 to here
# Normally it should be ok to just remove some of the patches like this:
rm *-mips*
rm *-phy*
rm a*
rm 880-gateworks_system_controller.patch
#But in case there are still errors on the make target/linux/{clean,prepare} V=99 Stage,
#remove all files except these, keep these files: (openwrt specific patches)
200-fix_localversion.patch 621-sched_act_connmark.patch
201-extra_optimization.patch 630-packet_socket_type.patch
202-reduce_module_size.patch 640-bridge_no_eap_forward.patch
210-darwin_scripts_include.patch 641-bridge_always_accept_eap.patch
211-stddef_include.patch 642-bridge_port_isolate.patch
212-byteshift_portability.patch 643-bridge_remove_ipv6_dependency.patch
220-module_exports.patch 644-bridge_optimize_netfilter_hooks.patch
230-openwrt_lzma_options.patch 650-pppoe_header_pad.patch
250-netfilter_depends.patch 651-wireless_mesh_header.patch
251-sound_kconfig.patch 652-atm_header_changes.patch
252-mv_cesa_depends.patch 653-disable_netlink_trim.patch
253-ssb_b43_default_on.patch 655-increase_skb_pad.patch
254-textsearch_kconfig_hacks.patch 900-slab_maxsize.patch
255-lib80211_kconfig_hacks.patch 910-kobject_uevent.patch
256-crypto_add_kconfig_prompts.patch 911-kobject_add_broadcast_uevent.patch
257-wireless_ext_kconfig_hack.patch 920-unable_to_open_console.patch
258-netfilter_netlink_kconfig_hack.patch 921-use_preinit_as_init.patch
260-move_bcm963xx_tag.patch 930-crashlog.patch
600-netfilter_layer7_2.22.patch 940-ocf_kbuild_integration.patch
601-netfilter_layer7_pktmatch.patch 941-ocf_20120127.patch
602-netfilter_layer7_match.patch 950-vm_exports.patch
603-netfilter_layer7_2.6.36_fix.patch 960-decompress_unlzo_fix.patch
604-netfilter_cisco_794x_iphone.patch 970-remove-unsane-filenames-from-deps_initramfs-list.patch
610-netfilter_match_bypass_default_checks.patch 980-arm_openwrt_machtypes.patch
611-netfilter_match_bypass_default_table.patch 992-mpcore_wdt_fix_watchdog_counter_loading.patch
612-netfilter_match_reduce_memory_access.patch 993-mpcore_wdt_fix_wdioc_setoptions_handling.patch
613-netfilter_optional_tcp_window_check.patch 994-mpcore_wdt_fix_timer_mode_setup.patch
620-sched_esfq.patch

#Make
cd ~/rpi_openwrt/openwrt/
make menuconfig # Choose BCM2708 Chipset, Raspberry Pi Board, Exit and Save
make target/linux/{clean,prepare} V=99 # does extract kernel and patch it
make kernel_oldconfig # builds some tools
make kernel_menuconfig # configures kernel
make menuconfig # to change RPi Patterns, i.e.:
# Packages rep:
# Image configuration -> Version configuration options -> Release Repo to:
# http://downloads.openwrt.org/attitude_adjustment/12.09/%T/generic/packages
# Main Partition Size from 48 to 64:
# Target Options -> Root File System Size, change from 48 to 64 MB or more
# Exit and Save
make V=99 -j 3

Files are in ~/rpi_openwrt/openwrt/bin/brcm2708
( i.e. openwrt-brcm2708-sdcard-vfat-ext4.img )
New build:
make kernel_menuconfig
make menuconfig
make V=99 -j 3

Inspiration and Help:
http://wiki.openwrt.org/doc/howto/build
https://code.google.com/p/raspberrypi-openwrt/issues/detail?id=11