build: call satisified? before modifying env.

[ilovezfs]

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• Have you checked to ensure there aren't other open Pull Requests for the same change?
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Requirement#modify_build_environment may depend on the side effects of
Requirement#satisfied?, so make sure the latter is called at least once
for each requirement during formula installation. Prior to b70b542,
Requirement#satisfied? would usually be called during Build#expand_reqs,
but that is longer the case.

[ilovezfs]

Right now, JAVA_HOME is no longer getting set during def install, which leads to failures like https://jenkins.brew.sh/job/Homebrew%20Core%20Pull%20Requests/16982/version=high_sierra/console