>It is not currently possible to build the LZ4 code on ARM, so let's
>remove that option in Kconfig for now.
>
>lib/built-in.o: In function `lz4_compress64kctx':
> lib/lz4/lz4_compress.c:339: undefined reference to `__ctzsi2'
>lib/built-in.o: In function `lz4_compressctx':
> lib/lz4/lz4_compress.c:157: undefined reference to `__ctzsi2'
>lib/built-in.o: In function `lz4hc_commonlength':
> lib/lz4/lz4hc_compress.c:102: undefined reference to `__ctzsi2'
> lib/lz4/lz4hc_compress.c:102: undefined reference to `__ctzsi2'
>lib/built-in.o: In function `lz4hc_insertandgetwidermatch':
> lib/lz4/lz4hc_compress.c:230: undefined reference to `__ctzsi2'

Please, let me know the gcc version and tested defconfig.
I didn't have any problem to build with gcc 4.6.4 on armv7.
Some architecture need libgcc functions for __builtin_clz/ctz.
Porting them to lib is in progress:
http://marc.info/?l=linux-kernel&m=136748861811956&w=2
But, It doesn't happen on ARM, PowerPC and x86.

Thanks
Chanho Min