fixing CMakeLists for non-x86 architectures

[Bl4omArchie]

As requested in issue #774, I added a condition in the CMakeLists so non-x86 can run the test. As I didn't have non-x86 archi, I hope this work.
Also I the opened issue other errors where reported like this one:

[ 97%] Building C object CMakeFiles/test_aesni.dir/test_aesni.c.o
[...]/src/test/test_aesni.c:2:10: fatal error: wmmintrin.h: No such file or directory
2 | #include <wmmintrin.h>
| ^~~~~~~~~~~~~

Maybe we should add directive for packages that aren't supported.

[Legrandin]

Thanks, I merged after a small refactoring, with "i686" (for 32-bit builds) and after making an AESNI test optional.