Debug info: use the file a typedef is defined in as its decl_file instead
of the current compilation unit.
As a side effect this enables many more LTO uniquing opportunities.

rdar://problem/15851206

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199757 91177308-0d34-0410-b5e6-96231b3b80d8