ENH: Fix pointer size determination for cross build
ENH: Fix pointer size determination for cross build

Using `sys` to ask about the build Python is hostile to cross
building because it is very hard to replace the sys module with one
that gives info about the target system. On the other hand, the
sysconfig data can be replaced by setting _PYTHON_SYSCONFIGDATA_NAME.
So instead of using `sys.maxsize` to determine pointer size, use
`sysconfig.get_config_var("SIZEOF_VOID_P")`

mattip/numpy,rgommers/numpy,mattip/numpy,numpy/numpy,anntzer/numpy,pdebuyl/numpy,rgommers/numpy,pdebuyl/numpy,numpy/numpy,numpy/numpy,mhvk/numpy,rgommers/numpy,pdebuyl/numpy,pdebuyl/numpy,mattip/numpy,rgommers/numpy,charris/numpy,mhvk/numpy,endolith/numpy,mhvk/numpy,anntzer/numpy,charris/numpy,charris/numpy,mhvk/numpy,numpy/numpy,anntzer/numpy,endolith/numpy,mattip/numpy,charris/numpy,endolith/numpy,mhvk/numpy,anntzer/numpy,endolith/numpy