Import obstack.c and obstack.h am: 61a263b27f am: 41994c0bcc am: 4a4da698d4

Original change: https://android-review.googlesource.com/c/platform/external/obstack/+/1843833

Change-Id: I549a80f86eccc118f98881861be87fb5119484c0
tree: 4bf158aad52e1579720839f76306df099af3144e
  1. include/
  2. libiberty/