Update configure.ac for binutils 2.25

Commit 073e8fa7 requires binutils 2.25
or later to build glibc:

	* configure.ac (AS): Require binutils 2.25 or later.
	(LD): Likewise.

But it only updated LD version check in configure.ac.  This patch adds
the missing AS version check.

	* configure.ac (AS): Require binutils 2.25 or later.
	* configure: Regenerated.