Rename module '_Noreturn' to 'snippet/_Noreturn'.

* modules/snippet/_Noreturn: Renamed from modules/_Noreturn.
(Files, Makefile.am): Update.
* build-aux/snippet/_Noreturn.h: Renamed from build-aux/_Noreturn.h.
* modules/stdlib (Depends-on): Update.

modules/snippet/_Noreturn

@@ -0,0 +1,27 @@
+Description:
+The _Noreturn keyword of C1X.
+
+Applicability:
+all
+
+Files:
+build-aux/snippet/_Noreturn.h
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+# Because this Makefile snippet defines a variable used by other
+# gnulib Makefile snippets, it must be present in all Makefile.am that
+# need it. This is ensured by the applicability 'all' defined above.
+
+_NORETURN_H=$(top_srcdir)/build-aux/snippet/_Noreturn.h
+
+Include:
+
+License:
+LGPLv2+
+
+Maintainer:
+all