That prevents the linker from dead-stripping the function, as it is not called
directly, it is resolved in the runtime via dlsym().

Bug: chromium:754124, chromium:787723
Change-Id: I46a02ef01349f59b7ed944ce1483b7277e234a19
Reviewed-on: https://chromium-review.googlesource.com/833995
Commit-Queue: Max Moroz <mmoroz@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50212}