Sync top-level configure.ac with binutils-gdb

	Sync with binutils-gdb:
	2015-10-21  Nick Clifton  <nickc@redhat.com>

	PR gas/19109
	* configure.ac: Note the 'none' is an acceptable argument to
	--enable-compressed-debug-sections.
	* configure: Regenerate.

From-SVN: r232279