libgui: Enable -Weverything and -Werror

Enables -Weverything and -Werror, with just a few exceptions for
warnings we can't (or shouldn't need to) work around.

Cherry pick of I034abec27bf4020d84af60d7acc1939c59986dd6 plus a
couple of minor changes to CpuConsumer.cpp to make it work with a
prior change:
    Uncomment CC_LOGV on line 46
    Change C-style cast to static_cast on line 71

Change-Id: Iaec610477ea0122317b0578fb74caf2383d4cf08