Debug Info: Prevent DW_AT_abstract_origin from being emitted twice

for the same subprogram.

This fixes a bug where DW_AT_abstract_origin is being emitted twice for
the same subprogram if a function is both inlined and emitted in the same
translation unit, by restoring the pre-r266446 behavior.

http://reviews.llvm.org/D20072

llvm-svn: 269103