TUKLIB_FAST_UNALIGNED_ACCESS must not be defined in src/lib/liblzma/config.h on strict alignment architectures

[crest]

I noticed that /usr/bin/xz crashed with signal 10 on a Feroceon 
88FR131 rev 1 CPU and traced back to an unaligned 16 bit memory access 
in liblzma. This is enabled by TUKLIB_FAST_UNALIGNED_ACCESS in 
src/lib/liblzma/config.h. Uncommenting this line fixed the problem. 
This may cost some performance on non strict aligment architectures 
(e.g. x86, most ppc). Passing it via CFLAGS instead of config.h based 
on architecture would fix this problem.