i didn't test ati-fglrx extensions in an 64 bit system, but you need toolchain64 extension and tc linux kernel src patched and installed for building any kernel module, that's quite complicated for a standart user to do unfortunately, wish there was a linux-headers-* for tc 64 too
steps to do in summary
1) download linux src patched and related config file
http://distro.ibiblio.org/pub/linux/distributions/tinycorelinux/3.x/release/src/kernel/2) load compiletc + toolchain64 extensions and open up a toolchain64 shell
3) extract linux src patched, cd to linux src, and move config file into linux src with name .config
4) prepare linux src for compiling modules
export ARCH=x86_64 CROSS_COMPILE=x86_64-unknown-linux-gnu-
make oldconfig
make modules_prepare
6) create system symlinks for pointing to linux src installation
sudo mkdir -p /usr/src
sudo ln -sf /path/to/linux/src /usr/src/linux
sudo ln -sf /usr/src/linux /lib/modules/`uname -r`/kernel/build
then you should be able compile ati fglrx kernel module by a simple make command