[sanitizer] Small tweaks and fixes to allocator related functions

Summary:
In `sanitizer_allocator_primary32.h`:
- rounding up in `MapWithCallback` is not needed as `MmapOrDie` does it. Note
  that the 64-bit counterpart doesn't round up, this keeps the behavior
  consistent;
- since `IsAligned` exists, use it in `AllocateRegion`;
- in `PopulateFreeList`:
  - checking `b->Count` to be greater than 0 when `b->Count() == max_count` is
    redundant when done more than once. Just check that `max_count` is greater
    than 0 out of the loop; the compiler (at least on ARM) didn't optimize it;
  - mark the batch creation failure as `UNLIKELY`;

In `sanitizer_allocator_primary64.h`:
- in `MapWithCallback`, mark the failure condition as `UNLIKELY`;

In `sanitizer_posix.h`:
- mark a bunch of Mmap related failure conditions as `UNLIKELY`;
- in `MmapAlignedOrDieOnFatalError`, we have `IsAligned`, so use it; rearrange
  the conditions as one test was redudant;
- in `MmapFixedImpl`, 30 chars was not large enough to hold the message and a
  full 64-bit address (or at least a 48-bit usermode address), increase to 40.

Reviewers: alekseyshl

Reviewed By: alekseyshl

Subscribers: aemerson, kubamracek, kristof.beyls, llvm-commits

Differential Revision: https://reviews.llvm.org/D34840

llvm-svn: 306834