build: 'make clean' doesn't delete os-config.tmpl.

Fixes <http://bugs.gnu.org/18243>.
Reported by Andreas Enge and Mark H. Weaver.

* Makefile.am (EXAMPLES): New variable.
  (nobase_dist_guilemodule_DATA): Add it.
* gnu-system.am (GNU_SYSTEM_MODULES): Remove gnu/system/os-config.tmpl.

Makefile.am

@@ -107,9 +107,13 @@ KCONFIGS =					\
   gnu/packages/linux-libre-i686.conf		\
   gnu/packages/linux-libre-x86_64.conf
 
+# Templates, examples.
+EXAMPLES =					\
+  gnu/system/os-config.tmpl
+
 GOBJECTS = $(MODULES:%.scm=%.go) guix/config.go
 
-nobase_dist_guilemodule_DATA = $(MODULES) $(KCONFIGS)
+nobase_dist_guilemodule_DATA = $(MODULES) $(KCONFIGS) $(EXAMPLES)
 nobase_nodist_guilemodule_DATA = $(GOBJECTS) guix/config.scm
 
 # Do we need to provide our own non-broken (srfi srfi-37) module?

gnu-system.am

@@ -269,7 +269,6 @@ GNU_SYSTEM_MODULES =				\
   gnu/system/file-systems.scm			\
   gnu/system/grub.scm				\
   gnu/system/install.scm			\
-  gnu/system/os-config.tmpl			\
   gnu/system/linux.scm				\
   gnu/system/linux-initrd.scm			\
   gnu/system/shadow.scm				\