Fix the return type of the getentropy stub

The return type of the getentropy stub is wrongly defined as ssize_t,
while both the <sys/random.h> header and the Linux implementation
define it as int. This patch fixes that.

Changelog:
	* stdlib/getentropy.c (getentropy): Change return type to int.

stdlib/getentropy.c

@@ -21,7 +21,7 @@
 
 /* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
    success and -1 on failure.  */
-ssize_t
+int
 getentropy (void *buffer, size_t length)
 {
   __set_errno (ENOSYS);