[sanitizer] simplify the allocator's SizeClassMap: do not require an extra template parameter, instead compute it in flight. No functionality change

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176853 91177308-0d34-0410-b5e6-96231b3b80d8
[msan] Use sptr instead of ptrdiff_t.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@176854 91177308-0d34-0410-b5e6-96231b3b80d8