erasure-code: SSE optimized jerasure plugins

The jerasure plugin is compiled with three sets of flags:

* jerasure_generic with no SSE optimization
* jerasure_sse3 with SSE2, SSE3 and SSSE3 optimizations
* jerasure_sse4 with SSE2, SSE3, SSSE3, SSE41, SSE42 and PCLMUL optimizations

The jerasure plugin loads the appropriate plugin depending on the CPU
features detected at runtime.

Signed-off-by: Loic Dachary <loic@dachary.org>