ext: Stop using the uninitialized pythonMain in sst.

Import the __main__ module when it's first used.

Change-Id: If800bd575398970faa8cb88072becd3d2b4218c0
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/54307
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
2 files changed