[asan] Teach asan_symbolize.py to use :arch with atos and llvm-symbolizer on Darwin

This patch teaches asan_symbolize.py to read an architecture suffix on module names (e.g. ":x86_64") and pass that option to atos and llvm-symbolizer.

Differential Revision: https://reviews.llvm.org/D27378

llvm-svn: 291280