Dalvik: Better compatibility with different compilers

This fixes building with clang 3.4, and possibly future versions of gcc:
- Don't error out on unused functions generated by gen-mterp.py
  even when we're using -Werror
- Eliminate some dead code (Word/kWordSize definition) clang warns about

Change-Id: I2874c6f05186721636518e422b0f39a3d8e731cd
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>