`csp` can't be cross-compiled due to use of `_csptypesimpl` during the build

[timkpaine]

Because _csptypesimpl is used during the build, if it is cross-compiled to a different arch it won't be useable. So during the build we should either:

• compile it for universal2 on Mac which will be useable everywhere, but won't work on linux since the equivalent doesn't really exist
• compile it for native for the build, then cross compile it just for distribution

xref: conda-forge/csp-feedstock#27