Remove Windows special-casing in openlibm and openspecfun install

openspecfun now needs headers from openlibm, and these were not getting installed on Windows

Bump openlibm and openspecfun

ref #6063 and #6295
Merge pull request #6459 from tkelman/patch-4

Remove Windows special-casing for openlibm and openspecfun installation (and bump them)