[sanitizer] Align & pad the allocator structures to the cacheline size v2

Summary:
This is a new version of D44261, which broke some builds with older gcc, as
they can't align on a constexpr, but rather require an integer (see
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56859) among others.

We introduce `SANITIZER_CACHE_LINE_SIZE` in `sanitizer_platform.h` to be
used in `ALIGNED` attributes instead of using directly `kCacheLineSize`.

Reviewers: alekseyshl, thakis

Reviewed By: alekseyshl

Subscribers: kubamracek, delcypher, #sanitizers, llvm-commits

Differential Revision: https://reviews.llvm.org/D44326

llvm-svn: 327297