Object: Teach irsymtab::read() to try to use the irsymtab that we wrote to disk.

Fixes PR27551.

Differential Revision: https://reviews.llvm.org/D33974

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306488 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed