configure.ac : Improve asm optimisation detection.
configure.ac : Improve asm optimisation detection.

When compiling for ia32 on an x86_64 kernel, the configure script
was not detecting the ability to do asm optimisations because the
configure script was detecting the x86_64 kernel not the ia32
user space.

fredericgermain/flac,waitman/flac,fredericgermain/flac,waitman/flac,fredericgermain/flac,fredericgermain/flac,waitman/flac,waitman/flac,waitman/flac