-Wunused-private-field warnings

Fairly recently clang picked up a -Wunused-private-field warning that does what you would expect. Compiling LLVM and clang with a recent clang spits out the following warnings:

http://pastie.org/private/lfdyj5prtbkyrvhddi40dq

–Sean Silva

Ah, I missed those when cleaning up LLVM because they are only unused in Release builds. Fixed in r158608/r158609.

- Ben