Use fewer processes while building OpenBLAS

[eschnett]

Closes #15716

[tkelman]

you'll have to delete this patch, and update the checksums if we're going to update to 0.2.17

[tkelman]

make -C deps NO_GIT=1 configure-openblas && git rm -r deps/checksums/openblas-53e849f4fcae4363a64576de00e982722c7304f9.tar.gz && git add deps/checksums/openblas-a71e8c82f6a9f73093b631e5deab1e8da716b61f.tar.gz

[eschnett]

Thanks for the pointer to these other checksums.

[tkelman]

Note that we should probably merge this in very close succession with #15724 if we want to do both of them, since either in isolation will cause an openblas rebuild. (so will merging both close together, but at least it'll be a single rebuild instead of two)

[tkelman]

upstream merged patch in OpenMathLib/OpenBLAS#829 was a little different, uses a different flag name

[eschnett]

@tkelman We can apply the patch nonetheless; once a new version of OpenBLAS is released, we will remove our patch anyway.

[tkelman]

But the upstream patch uses a different name for the make flag. So we'd need to change. Let's use a patch that matches what we will get from upstream so the flag can match as well.

[eschnett]

Now using the upstream commit as patch.

[tkelman]

Cool. I'm okay with this version, but for the sake of not making everyone rebuild openblas twice let's see if there are any objections to #15724.