lib/clz_ctz.c: add prototype declarations in lib/clz_ctz.c

Add prototype declarations of functions in lib/clz_ctz.c. These
functions are required by GCC builtins and hence can not be removed
despite of their unreferenced appearance in kernel source.

This eliminates the following warning in lib/clz_ctz.c:

lib/clz_ctz.c:16:12: warning: no previous prototype for `__ctzsi2' [-Wmissing-prototypes]
lib/clz_ctz.c:22:12: warning: no previous prototype for `__clzsi2' [-Wmissing-prototypes]
lib/clz_ctz.c:44:12: warning: no previous prototype for `__clzdi2' [-Wmissing-prototypes]
lib/clz_ctz.c:50:12: warning: no previous prototype for `__ctzdi2' [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <[e-mail]>
Reviewed-by: Josh Triplett <[e-mail]>
Acked-by: Chanho Min <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/clz_ctz.c

···
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
+ * The functions in this file aren't called directly, but are required by
+ * GCC builtins such as __builtin_ctz, and therefore they can't be removed
+ * despite appearing unreferenced in kernel source.
  *
  * __c[lt]z[sd]i2 can be overridden by linking arch-specific versions.
  */
···
 #include <linux/export.h>
 #include <linux/kernel.h>
 
+int __weak __ctzsi2(int val);
 int __weak __ctzsi2(int val)
 {
 	return __ffs(val);
 }
 EXPORT_SYMBOL(__ctzsi2);
 
+int __weak __clzsi2(int val);
 int __weak __clzsi2(int val)
 {
 	return 32 - fls(val);
 }
 EXPORT_SYMBOL(__clzsi2);
 
+int __weak __clzdi2(long val);
+int __weak __ctzdi2(long val);
 #if BITS_PER_LONG == 32
 
 int __weak __clzdi2(long val)