util-m5: Fix Scons exports when building the m5 utility

The name of the imported environment in ext/googletest/SConscript was
changed from `main` to `env` in [1].

Updated the `exports` when building the `m5` utility to export the
correct name.

[1] https://gem5-review.googlesource.com/c/public/gem5/+/56750

Change-Id: I195b760e9092fbe63e5de1316403e090c1fa4e1f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57909
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed