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In particular LLVM_SYMBOLIZER_PATH is needed by asan_symbolize.py.

Also explicitly wait for test launcher to finish running and use its return
code as an overall exit code of the test. asan_symbolize.py always returns
0 (if it doesn't crash), not very useful.

BUG=424280
R=earthdok@chromium.org

Review URL: https://codereview.chromium.org/639713009

Cr-Commit-Position: refs/heads/master@{#300252}