[sanitizer] change the 64-bit allocator to use a single array for free-d...

[sanitizer] change the 64-bit allocator to use a single array for free-d chunks instead of a lock-free linked list of tranfer batches. This change simplifies the code, makes the allocator more 'hardened', and will allow simpler code to release RAM to OS. This may also slowdown malloc stress tests due to lock contension, but I did not observe noticeable slowdown on various real multi-threaded benchmarks.

llvm-svn: 279572