[tsan] Use malloc zone interceptors on OS X, part 1 (refactoring)

TSan needs to use a custom malloc zone on OS X, which is already implemented in ASan.  This patch is a refactoring patch (NFC) that extracts this from ASan into sanitizer_common, where we can reuse it in TSan.

Reviewed at http://reviews.llvm.org/D14330

llvm-svn: 252052