getline: split out for darwin systems

At least on OS X 10.5 and older, getline does not exist.  So split out the
function from the mingw code so that we can pull it in for Darwin systems.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/tools/os_support.h b/tools/os_support.h
index 7bf930e..7dcbee4 100644
--- a/tools/os_support.h
+++ b/tools/os_support.h
@@ -28,4 +28,8 @@
 #include "mingw_support.h"
 #endif
 
+#ifdef __APPLE__
+#include "getline.h"
+#endif
+
 #endif /* __OS_SUPPORT_H_ */