Support of AVX build for linux

By default, it will use march=native to optimize on the current build. It requires GCC 4.7. A runtime detection will be nicer but more complex to implement. I let others contributors to implement it ;) At least it is now possible to use full AVX on linux.

I keep a way to disable this update for older GCC and portable distribution (DISABLE_ADVANCE_SIMD=TRUE).

GSVector must be review carefully and tested on windows (if it still compile)