getty: trigger /etc/issue compat mode for Alpine Linux

The /etc/issue file on Alpine Linux says "Kernel \r on an \m (\l)", so
\r needs to return the uts release rather than os-release VERSION.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/getty.c

@@ -121,6 +121,9 @@ static int osrel(struct osrel *rel)
 			snprintf(rel->version, sizeof(rel->version), "(%s)", codename);
 	}
 
+	if (rel->id[0] && !strcmp(rel->id, "alpine"))
+		return 1;	/* compat mode for \r et al. */
+
 	return 0;
 }