Fix missing prototype warning in utf-conv.c
diff --git a/src/win32/utf-conv.c b/src/win32/utf-conv.c
index 3c8be81..683b883 100644
--- a/src/win32/utf-conv.c
+++ b/src/win32/utf-conv.c
@@ -7,6 +7,7 @@
#include "common.h"
#include "utf-conv.h"
+#include "git2/windows.h"
/*
* Default codepage value