Investigate efficiency of gcc builtin sigma functions and analyse generated code

[gut]

Functions like __builtin_crypto_vshasigmaw can be used directly by gdb. By looking at the output with -O3 it may give us better insight of how to best develop this functionality for ppc64le on other projects.

[racardoso]

I do some little changes on this code ad50124 It's a optimization idea. Since I'll have to check any performance issues with this optimization candidate we can work together on this issue.

[brunoalr]

Closing this issue since we killed everything except for the asm versions.