Fix EINTR handling in Unix stdin pipe hack

extra/io/unix/backend/backend.factor

@@ -168,7 +168,7 @@ M: stdin dispose
 
 : wait-for-stdin ( stdin -- n )
     [ control>> CHAR: X over io:stream-write1 io:stream-flush ]
-    [ size>> "size_t" heap-size swap io:stream-read *uint ]
+    [ size>> "ssize_t" heap-size swap io:stream-read *int ]
     bi ;
 
 :: refill-stdin ( buffer stdin size -- )

vm/os-unix.c

@@ -339,7 +339,7 @@ void *stdin_loop(void *arg)
 
 		for(;;)
 		{
-			size_t bytes = read(0,buf,sizeof(buf));
+			ssize_t bytes = read(0,buf,sizeof(buf));
 			if(bytes < 0)
 			{
 				if(errno == EINTR)