Add altivec support (smx, IBM Power 8)
Targeting open power arch, we start porting the inastemp simd class to altivec.
It is currently a work in progress.
* [x] Manage load/store (especially not alligned)
* [x] Manage little/big Indian (in the load/store and the signof)
* [x] Build with XL compiler
See merge request !3