sys/linux: Add binding to ioctl syscall + fd consts

Add binding to ioctl syscall, due to the vast nature of this syscall
adding more device specific request values is possible. Also added the
stdin, stdout and stderr, to constants.odin

core/sys/linux/constants.odin

@@ -1,6 +1,21 @@
 
 package linux
 
+/*
+	Standard input file descriptor
+*/
+STDIN_FILENO :: Fd(0)
+
+/*
+	Standard output file descriptor
+*/
+STDOUT_FILENO :: Fd(1)
+
+/*
+	Standard output file descriptor
+*/
+STDERR_FILENO :: Fd(2)
+
 /*
 	Special file descriptor to pass to `*at` functions to specify
 	that relative paths are relative to current directory.