[GWP-ASan] Add mutexes for Fuchsia am: 6e469b1c55 am: 0decae2d2b

Original change: https://android-review.googlesource.com/c/platform/external/gwp_asan/+/1506411

Change-Id: I3a4db3316d268b5c3d57bddb41ef7c8043afa502