In order to support Mac OS X builds on RelEng, we need to upgrade the Clang version used for ASan. Right now, I'm testing with r214699, but this revision might change as we might discover more problems that need fixing in ASan itself. I will upload builds for Linux and Mac once local testing is complete. We should then make these builds available on RelEng hosts so we can do try runs with them before switching to the new version.
The static analysis builds are using a newer clang, you could try that: https://dxr.mozilla.org/mozilla-central/source/browser/config/tooltool-manifests/macosx64/clang.manifest
Presumably we'd upgrade to a more modern version now, as in bug 1267650 or bug 1214463.