recovery: Switch to clang

And a few trival fixes to suppress warnings.

Change-Id: I38734b5f4434643e85feab25f4807b46a45d8d65
diff --git a/uncrypt/Android.mk b/uncrypt/Android.mk
index d832d97..6859e75 100644
--- a/uncrypt/Android.mk
+++ b/uncrypt/Android.mk
@@ -16,6 +16,8 @@
 
 include $(CLEAR_VARS)
 
+LOCAL_CLANG := true
+
 LOCAL_SRC_FILES := uncrypt.cpp
 
 LOCAL_MODULE := uncrypt