binfmt_elf: compat: avoid unused function warning

When CONFIG_ELF_CORE is disabled, we get a harmless warning in the compat
version of binfmt_elf:

fs/compat_binfmt_elf.c:58:13: error: 'cputime_to_compat_timeval' defined but not used [-Werror=unused-function]

This was addressed in mainline Linux as part of a larger rework with commit
cd19c364 ("fs/binfmt: Convert obsolete cputime type to nsecs").

For 4.9 and earlier, this just shuts up the warning by adding an #ifdef
around the function definition.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/compat_binfmt_elf.c

@@ -51,6 +51,7 @@
 #define elf_prstatus	compat_elf_prstatus
 #define elf_prpsinfo	compat_elf_prpsinfo
 
+#ifdef CONFIG_ELF_CORE
 /*
  * Compat version of cputime_to_compat_timeval, perhaps this
  * should be an inline in <linux/compat.h>.
@@ -63,6 +64,7 @@ static void cputime_to_compat_timeval(const cputime_t cputime,
 	value->tv_sec = tv.tv_sec;
 	value->tv_usec = tv.tv_usec;
 }
+#endif
 
 #undef cputime_to_timeval
 #define cputime_to_timeval cputime_to_compat_timeval