You will find the precompiled version of the x86 toolchain from the TD-W8970 GPL tarball at the releases section.
export PATH=/your/path/to/toolchain-mips_r2_gcc-4.3.3+cs_uClibc-0.9.30.1_2_6_32/usr/bin/:$PATH
export ARCH=mips
export CROSS_COMPILE=mips-linux-
make distclean vr9_config
cp tdw8970.config .config
make oldconfig u-boot.lq u-boot.asc
After compiling, you will find the following files in your directory:
Please note that in case of an UART boot, the CPU will only run at 125MHz. So don't expect it to be as fast as usual.