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

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

Change-Id: Id48d8fdffd4b17792b8e5da408bd52bc4ab7ea59
tree: 4bf158aad52e1579720839f76306df099af3144e
  1. include/
  2. libiberty/