recovery: Switch to clang

And a few trival fixes to suppress warnings.

Change-Id: Id28e3581aaca4bda59826afa80c0c1cdfb0442fc
(cherry picked from commit 80e46e08de5f65702fa7f7cd3ef83f905d919bbc)
diff --git a/uncrypt/Android.mk b/uncrypt/Android.mk
index c7d4d37..e73c8f1 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