s390/module: fix building test_modules_helpers.o with clang

Move test_modules_return_* prototypes into a header file in order to
placate -Wmissing-prototypes.

Fixes: 90c5318795ee ("s390/module: test loading modules with a lot of relocations")
Reported-by: kernel test robot <[e-mail]>
Reviewed-by: Heiko Carstens <[e-mail]>
Signed-off-by: Ilya Leoshkevich <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>

arch/s390/lib/test_modules.c

···
 
 #include "test_modules.h"
 
-#define DECLARE_RETURN(i) int test_modules_return_ ## i(void)
-REPEAT_10000(DECLARE_RETURN);
-
 /*
  * Test that modules with many relocations are loaded properly.
  */

arch/s390/lib/test_modules.h

···
 	__REPEAT_10000_1(f, 8); \
 	__REPEAT_10000_1(f, 9)
 
+#define DECLARE_RETURN(i) int test_modules_return_ ## i(void)
+REPEAT_10000(DECLARE_RETURN);
+
 #endif