Possibility to also furnish an openmp based build #99

Since #87 and #88 seems to want to make an easier to use package for public use, I was also wondering if it would be possible to build in addition an openmp build? This is just changing a variable here https://github.com/MacPython/openblas-libs/blob/master/tools/build_openblas.sh#L91 and is already the official default for the homebrew version https://formulae.brew.sh/formula/openblas

It's also available in cent os 7 and recent ubuntus as both a pthread and openmp version, so I'd guess that any old issue where it used to hang is now fixed. Currently, using these libs made with pthread under another program which would use openmp simply spams the terminal with a lot of warnings asking to rebuild openblas with openmp support, making it unusable and much, much slower. Just a suggestion that any other public project wanting to use this and openmp is currently unable to do so because of this issue.