pivot_root.c: move prototype into guard

Signed-off-by: Peter S. Mazinger <ps.m@gmx.net>
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>

libc/sysdeps/linux/common/pivot_root.c

@@ -9,7 +9,7 @@
 
 #include <sys/syscall.h>
 
-int pivot_root(const char *new_root, const char *put_old);
 #ifdef __NR_pivot_root
+int pivot_root(const char *new_root, const char *put_old);
 _syscall2(int, pivot_root, const char *, new_root, const char *, put_old)
 #endif