[sanitizer] use fewer size classes in the allocator to reduce the memory footprint. There is no all-size-fits-all constant here, but this change is positive or neutral on several large apps I've tested

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176855 91177308-0d34-0410-b5e6-96231b3b80d8