obstack-printf-gnu: Fix mistake (reported by check-AC_LIBOBJ)

[Bruno Haible]

I happened to run 'check-AC_LIBOBJ':

  $ ./check-AC_LIBOBJ
  modules/obstack-printf-gnu lacks file lib/obstack_printf.c

This patch fixes it.


2024-08-29  Bruno Haible  <bruno@clisp.org>

        obstack-printf-gnu: Fix mistake (reported by check-AC_LIBOBJ).
        * modules/obstack-printf-gnu (Files): Add lib/obstack_printf.c.

diff --git a/modules/obstack-printf-gnu b/modules/obstack-printf-gnu
index 3b51bed05e..f73d00f8cc 100644
--- a/modules/obstack-printf-gnu
+++ b/modules/obstack-printf-gnu
@@ -9,6 +9,7 @@ that module occurs among the main modules in lib/.
 
 Files:
 m4/obstack-printf-gnu.m4
+lib/obstack_printf.c
 
 Depends-on:
 obstack-printf-posix