GCC 4.6 (in dalvik-dev) is stricter about converting from NULL.

Fix the LLVM build for dalvik-dev.

Change-Id: I35636b971453c2977b39ff840c2960c63ad658d6
diff --git a/src/compiler_llvm/stub_compiler.cc b/src/compiler_llvm/stub_compiler.cc
index 2cf5141..a94a5ad 100644
--- a/src/compiler_llvm/stub_compiler.cc
+++ b/src/compiler_llvm/stub_compiler.cc
@@ -196,7 +196,7 @@
                                        char const* shorty) {
   // Static method dosen't need proxy stub.
   if (is_static) {
-    return NULL;
+    return 0;
   }
 
   CHECK_NE(shorty, static_cast<char const*>(NULL));