math/openblas: Fix build on 12-CURRENT armv6.

The build still fails on 11 armv6, however MFC of r313873 will hopefully
fix the build there as well.

While here also add LICENSE_FILE and fix portlint warnings.

PR: 217279
Submitted by: mikael.urankar@gmail.com
Approved by: phd_kimberlite@yahoo.co.jp (maintainer), swills (mentor, implicit)
Differential Revision: https://reviews.freebsd.org/D9801