This was accidentally removed in aosp/2094705. Among other possible
issues, this caused the "used environment variable" file to be omitted
from the depfile of soong_build during mixed builds, which would result
in soong_build not being subsequently retriggered during env var
changes.
Sendng this out as a quickfix, regression test to follow.
Bug: 233774464
Test: Manual `m nothing && USE_BAZEL_ANALYSIS=1 m nothing && m nothing`,
verifying that a rebuild was retriggered in each invocation.
Change-Id: I1d9dbd1bc4696df760ebb9be262bc165c161bb21
027881cf35