Revert "Revert "Load env variables before c.config()""

This reverts commit 4e88859a.

Reason for revert: Given https://googleplex-android-review.git.corp.google.com/c/platform/build/soong/+/15747538, we should be able to rollforward with this now.

Bug: b/198045383
Change-Id: I4c069e952d9f77258433b5059f3867293993a64d