Rename __asan_gen_* symbols to ___asan_gen_*.

This prevents gold from printing a warning when trying to export
these symbols via the asan dynamic list after ThinLTO promotes them
from private symbols to external symbols with hidden visibility.

Differential Revision: https://reviews.llvm.org/D49498

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337428 91177308-0d34-0410-b5e6-96231b3b80d8
10 files changed