ART: More warnings

Enable -Wno-conversion-null, -Wredundant-decls and -Wshadow in general,
and -Wunused-but-set-parameter for GCC builds.

Change-Id: I81bbdd762213444673c65d85edae594a523836e5
diff --git a/disassembler/disassembler_arm64.h b/disassembler/disassembler_arm64.h
index ad20c70..e56fe4f 100644
--- a/disassembler/disassembler_arm64.h
+++ b/disassembler/disassembler_arm64.h
@@ -19,8 +19,11 @@
 
 #include "disassembler.h"
 
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wshadow"
 #include "a64/decoder-a64.h"
 #include "a64/disasm-a64.h"
+#pragma GCC diagnostic pop
 
 namespace art {
 namespace arm64 {