Fixes: https://github.com/openwrt/packages/issues/15370

This is inspired from:
   330bc94dcc/lang/python-greenlet/Makefile

The `PKG_USE_MIPS16:=0` is not taken into consideration when building
Python modules. That's because the sysconfig is used.

This is only an issue with greenlet (on MIPS) so far.

One option is to do `PKG_USE_MIPS16:=0` in the core Python package.
But, since we know that the `wlanslovenija` group has successfully used
greenlet on MIPS with this construct, we might as well adopt it until GCC10
becomes the main compiler.

As noted here:
  https://github.com/openwrt/packages/issues/15370#issuecomment-817015484
GCC10 doesn't have this problem.

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

Notes:
Build is disabled for arc and mips because
greenlet isn't ported for these platforms

Signed-off-by: Jan Pavlinec <jan.pavlinec@nic.cz>