fix integer overflow in WIFSTOPPED macro

the result of the 0xffff mask with the exit status could have bit 15
set, in which case multiplying by 0x10001 overflows 32-bit signed int.
making the multiply unsigned avoids the overflow. it also changes the
sign extension behavior of the subsequent >> operation, but the
affected bits are all unwanted anyway and all discarded by the cast to
short.

include/stdlib.h

@@ -95,7 +95,7 @@ size_t __ctype_get_mb_cur_max(void);
 #define WTERMSIG(s) ((s) & 0x7f)
 #define WSTOPSIG(s) WEXITSTATUS(s)
 #define WIFEXITED(s) (!WTERMSIG(s))
-#define WIFSTOPPED(s) ((short)((((s)&0xffff)*0x10001)>>8) > 0x7f00)
+#define WIFSTOPPED(s) ((short)((((s)&0xffff)*0x10001U)>>8) > 0x7f00)
 #define WIFSIGNALED(s) (((s)&0xffff)-1U < 0xffu)
 
 int posix_memalign (void **, size_t, size_t);

include/sys/wait.h

@@ -50,7 +50,7 @@ pid_t wait4 (pid_t, int *, int, struct rusage *);
 #define WSTOPSIG(s) WEXITSTATUS(s)
 #define WCOREDUMP(s) ((s) & 0x80)
 #define WIFEXITED(s) (!WTERMSIG(s))
-#define WIFSTOPPED(s) ((short)((((s)&0xffff)*0x10001)>>8) > 0x7f00)
+#define WIFSTOPPED(s) ((short)((((s)&0xffff)*0x10001U)>>8) > 0x7f00)
 #define WIFSIGNALED(s) (((s)&0xffff)-1U < 0xffu)
 #define WIFCONTINUED(s) ((s) == 0xffff)