[BUG] Missing strrchr definition in arch/um/drivers/

The following error occurs when building with a x86_64 defconfig

In file included from /usr/include/features.h:540,
                 from /usr/include/sys/types.h:25,
                 from ./arch/um/include/shared/user.h:24,
                 from <command-line>:
arch/um/drivers/cow_user.c: In function ‘absolutize’:
arch/um/drivers/cow_user.c:156:17: error: implicit declaration of function ‘strrchr’ [-Wimplicit-function-declaration]
  156 |         slash = strrchr(from, '/');
      |                 ^~~~~~~
arch/um/drivers/cow_user.c:17:1: note: ‘strrchr’ is defined in header ‘<string.h>’; this is probably fixable by adding ‘#include <string.h>’
   16 | #include "cow_sys.h"
  +++ |+#include <string.h>
   17 |
arch/um/drivers/cow_user.c:156:15: error: assignment to ‘char *’ from ‘int’ makes pointer from integer without a cast [-Wint-conversion]
  156 |         slash = strrchr(from, '/');
      |               ^