Fix unwanted "hard" fallback to Prescott in runtime detection of Intel cpus

[martin-frbg]

fixes #4267

[ogrisel]

@jeromedockes can you please rebuild this branch of OpenBLAS on your host with DYNAMIC_ARCH enabled and check that the right architecture is detected (e.g. with threadpoolctl)?

[jeromedockes]

@ogrisel sorry for the delay. yes I confirm that the right architecture is detected now. I compiled this

#include <cblas.h>
#include <stdio.h>

void main() { printf("architecture: %s\n", openblas_get_corename()); }

with the develop branch of OpenBLAS (before this PR was merged) I get

architecture: Prescott

and with this branch I get

architecture: Haswell

(and in any case if I compile OpenBLAS without DYNAMIC_ARCH enabled I get architecture: HASWELL

[ogrisel]

Thanks very much for the confirmation !

[ogrisel]

And thanks @martin-frbg for the quick fix.