Copy gnulib obstack files

This copies obstack.[ch] from gnulib, and updates the docs.  The next
patch should be applied if someone repeats the import at a later date.

include/
	* obstack.h: Import current gnulib file.
libiberty/
	* obstack.c: Import current gnulib file.
	* obstacks.texi: Updated doc, from glibc's manual/memory.texi.

From-SVN: r229987

include/ChangeLog

+2015-11-09  Alan Modra  <amodra@gmail.com>
+
+	PR gdb/17133
+	* obstack.h: Import current gnulib file.
+
 2015-11-05  Jakub Jelinek  <jakub@redhat.com>
 	    Ilya Verbin  <ilya.verbin@intel.com>
 

libiberty/ChangeLog

+2015-11-09  Alan Modra  <amodra@gmail.com>
+
+	PR gdb/17133
+	* obstack.c: Import current gnulib file.
+	* obstacks.texi: Updated doc, from glibc's manual/memory.texi.
+
 2015-11-06  Joel Brobecker  <brobecker@adacore.com>
 
 	* configure.ac: Set AC_CV_FUNC_GETPAGESIZE to "yes" on