asan/tsan: reduce per-thread memory allocator caches
256 blocks (which is 512 in reallity) seems to be too big cache,
reducing the size reduces memory consumption but does not degrade performance.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@177502 91177308-0d34-0410-b5e6-96231b3b80d8