[asan][test] Fix use-after-scope-capture test after D148269

After enabling ArgPromotion at lower opt levels, the body of this test
was optimized away, and the CHECK lines no longer functioned.

Setting -O0 is a hammer, but gets the test passing again, until code owners
can find a better solution.

Reviewed By: fmayer

Differential Revision: https://reviews.llvm.org/D148396