build both tsan and msan libc++

std::call_once() will trigger false positive races without
a libc++ (specifically __call_once()) built with TSAN itself.

Interestingly, there's a built-in interceptor for this
use case, only on Mac: https://reviews.llvm.org/D24188.

Fixes: skia:9884
Change-Id: I7b2c031c15b78ec7302c42b4e4ac365d596c2c33
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/265567
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Ben Wagner aka dogben <benjaminwagner@google.com>
10 files changed