recovery: Switch to clang

And a few trival fixes to suppress warnings.

Change-Id: I38734b5f4434643e85feab25f4807b46a45d8d65
diff --git a/minzip/Android.mk b/minzip/Android.mk
index 045f355..48d26bc 100644
--- a/minzip/Android.mk
+++ b/minzip/Android.mk
@@ -16,6 +16,8 @@
 
 LOCAL_MODULE := libminzip
 
+LOCAL_CLANG := true
+
 LOCAL_CFLAGS += -Wall
 
 include $(BUILD_STATIC_LIBRARY)