python-greenlet: support MIPS architecture

python-greenlet: support MIPS architecture

Fixes: https://github.com/openwrt/packages/issues/15370
This is inspired from:
   https://github.com/wlanslovenija/firmware-packages-opkg/blob/330bc94dccd16a3e92ac2fdde08c81a598e12f94/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>