@druna....
Yes the debian based systems use mawk interpreter instead of gawk and i faced the same problem recently....
install gawk on ur host with apt-get install gawk
and if that dint work i think applying patch works.
Note

atch should be applied to host not the build system...
Btw i ve a doubt ...wheter we should touch the linux kernel tarball in the chapter 5 itself coz we need api headers to install...
But sum1 on the forum said that it shouldn't be touched until chp -8
Using:LFS-6.3
Build:i686
Host:Ubuntu,i686