core: Fix missing include in msgfile.c for getline

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/src/msgfile.c b/src/msgfile.c
index d2b180d..1a99184 100644
--- a/src/msgfile.c
+++ b/src/msgfile.c
@@ -28,6 +28,7 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <string.h>
+#include <stdio.h>
 
 static struct osmo_config_entry *
 alloc_entry(struct osmo_config_list *entries,