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/compiler/utils/arm/assembler_thumb2.cc b/compiler/utils/arm/assembler_thumb2.cc
index fd2613a..71d6e7e 100644
--- a/compiler/utils/arm/assembler_thumb2.cc
+++ b/compiler/utils/arm/assembler_thumb2.cc
@@ -2121,8 +2121,8 @@
         branch->ResetSize(Branch::k16Bit);
 
         // Now add a compare instruction in the place the branch was.
-        int16_t cmp = B13 | B11 | static_cast<int16_t>(branch->GetRegister()) << 8;
-        buffer_.Store<int16_t>(branch_location, cmp);
+        buffer_.Store<int16_t>(branch_location,
+                               B13 | B11 | static_cast<int16_t>(branch->GetRegister()) << 8);
 
         // Since have moved made a hole in the code we need to reload the
         // current pc.