PRESUBMIT: add check and test for fuzz targets to catch missing header include.

The header (testing/libfuzzer/libfuzzer_exports.h) should be included in fuzz
targets they define optional libFuzzer symbols, as otherwise those symbols may
be stripped by the linker on Mac and fuzz target may work incorrectly, see
https://crbug.com/687076 for more information.

Bug: 991345
Change-Id: I459774f2bc8de708d67c0af455031146592c4799
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1738756
Commit-Queue: Max Moroz <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Abhishek Arya <[email protected]>
Cr-Commit-Position: refs/heads/master@{#685342}
3 files changed