[scudo] Lock FallbackTSD before draining it

Differential Revision: https://reviews.llvm.org/D150301

Bug: 281740882

GitOrigin-RevId: 6561032e1d3c561b3f7ced817bf3350b8622bf92
Change-Id: I4225b1f9a9c4e353553c92627591f1f5695e9227
Mreged-In: I4225b1f9a9c4e353553c92627591f1f5695e9227
(cherry picked from commit c3ba0f1d13d228616f57a714a3fc28a1fae83b37)
1 file changed