Update amd64 GNU cpu regex in cputable to match amd64 too

FreeBSD outputs amd64 as the cpu, so we need to match that in addition
to x86_64.

cputable

@@ -17,7 +17,7 @@
 i386		i586		(i[34567]86|pentium)	32	little
 ia64		ia64		ia64			64	little
 alpha		alpha		alpha.*			64	little
-amd64		x86_64		x86_64			64	little
+amd64		x86_64		(amd64|x86_64)		64	little
 armeb		armeb		arm.*b			32	big
 arm		arm		arm.*			32	little
 arm64		aarch64		aarch64			64	little

debian/changelog

@@ -49,6 +49,8 @@ dpkg (1.18.0) UNRELEASED; urgency=low
   * Add dpkg --ctrl-tarfile forwarding command for dpkg-deb.
   * Disable dependency checks on dpkg-buildpackage -S -nc.
   * Make dependency checks fatal for dpkg-buildpackage -S.
+  * Update amd64 GNU cpu regex in cputable to match amd64 too, in addition
+    to x86_64. This is required for FreeBSD.
 
   * Perl modules:
     - Rename and deprecate Dpkg::Gettext _g function with new g_.