Fix compilation with clang-3.3

clang-3.3 is stricter regarding the second argument of _mm_shuffle_epi32.

Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>
Workaround missing bit_AES defines

clang provides the same constant as bit_AESNI in some versions, and doesn't
provide it at all in others.

Signed-off-by: Sebastian Ramacher <sebastian+dev@ramacher.at>
Clearer wording on Linux installation dependencies. One doesn't just require them if the build fails with a specific error. LP:1270996.