package/openblas: bump to version v0.3.20

This commit dropped a patch included upstream. The other patch was
rebased.

For change log since v0.3.18, see:
- https://github.com/xianyi/OpenBLAS/releases/tag/v0.3.19
- https://github.com/xianyi/OpenBLAS/releases/tag/v0.3.20



Signed-off-by: Julien Olivain <ju.o@free.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>