Add size for the $dexfile debug symbol.

Needed for libunwind to be able to find it.

Test: readelf on boot.oat
Change-Id: Ieaa5ee51a6786f7c6bf86c79fb7de0d0dc9cabaf
diff --git a/compiler/debug/elf_symtab_writer.h b/compiler/debug/elf_symtab_writer.h
index 95a0b4f..9007360 100644
--- a/compiler/debug/elf_symtab_writer.h
+++ b/compiler/debug/elf_symtab_writer.h
@@ -107,7 +107,8 @@
     for (auto it : debug_info.dex_files) {
       uint64_t dex_address = dex->GetAddress() + it.first /* offset within the section */;
       const DexFile* dex_file = it.second;
-      symtab->Add(strtab->Write(kDexFileSymbolName), dex, dex_address, 0, STB_LOCAL, STT_NOTYPE);
+      typename ElfTypes::Word dex_name = strtab->Write(kDexFileSymbolName);
+      symtab->Add(dex_name, dex, dex_address, dex_file->Size(), STB_LOCAL, STT_NOTYPE);
       if (mini_debug_info) {
         continue;  // Don't add interpreter method names to mini-debug-info for now.
       }