Use ifunc strategy or other ways to only check target feature existance once

[bluss]

See memchr code at https://github.com/BurntSushi/rust-memchr/blob/451d16d440928b5547b92317fd83fc4c937b7b91/src/x86/mod.rs

• Do we need to use this?
• Can we use this to select kernel and kernel parameters only once (mr & nr in particular).

[bluss]

Since #37 we only check target feature selection once per sgemm/dgemm call (doesn't make much of a difference per se), and we are ready for caching if it's needed.