gnu: linux-libre: Enable build for aarch64-linux.

* gnu/packages/linux.scm (%linux-compatible-systems): Add aarch64-linux.
  (linux-libre-4.14): Limit to x86_64-linux, i686-linux and armhf-linux.
* gnu/packages/aux-files/linux-libre/4.16-arm64.conf: New file.
* Makefile.am (AUX_FILES): Add 4.16-arm64.conf.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

Makefile.am

@@ -264,6 +264,7 @@ dist_noinst_DATA = guix/tests.scm guix/tests/http.scm
 AUX_FILES =						\
   gnu/packages/aux-files/emacs/guix-emacs.el		\
   gnu/packages/aux-files/linux-libre/4.16-arm.conf	\
+  gnu/packages/aux-files/linux-libre/4.16-arm64.conf	\
   gnu/packages/aux-files/linux-libre/4.16-i686.conf	\
   gnu/packages/aux-files/linux-libre/4.16-x86_64.conf	\
   gnu/packages/aux-files/linux-libre/4.14-arm.conf	\

gnu/packages/linux.scm

@@ -388,7 +388,7 @@ It has been modified to remove all non-free binary blobs.")
     (license license:gpl2)))
 
 (define %intel-compatible-systems '("x86_64-linux" "i686-linux"))
-(define %linux-compatible-systems '("x86_64-linux" "i686-linux" "armhf-linux"))
+(define %linux-compatible-systems '("x86_64-linux" "i686-linux" "armhf-linux" "aarch64-linux"))
 
 ;; linux-libre configuration for armhf-linux is derived from Debian armmp.  It
 ;; supports qemu "virt" machine and possibly a large number of ARM boards.
@@ -409,7 +409,7 @@ It has been modified to remove all non-free binary blobs.")
 (define-public linux-libre-4.14
   (make-linux-libre %linux-libre-4.14-version
                     %linux-libre-4.14-hash
-                    %linux-compatible-systems
+                    '("x86_64-linux" "i686-linux" "armhf-linux")
                     #:configuration-file kernel-config))
 
 (define-public linux-libre-4.9