[tsan] Allow symbolizers that don't obtain global symbol sizes

The default symbolizer, `llvm-symbolizer` provides sizes for global symbols. On OS X, we want to also allow using `atos` (because it's available everywhere and users don't need to copy/install it) and `dladdr` (it's the only available option when running in a sandbox). However, these symbolizers do not supply the symbol sizes, only names and starting addresses. This patch changes the reporting functions to hide the size of the symbol when this value is unavailable, and modifies tests to make this part of the report "optional".

Differential Revision: http://reviews.llvm.org/D14608

llvm-svn: 252896