Add a new imgdiag tool to diff boot.art/core.art against a process

Analyze the dirty memory pages of a running process per-object,
this allows is to to fine-tune the dirty object binning algorithm in
image writer.

Also:
* Factor out oatdump command line parsing code into cmdline.h
* Factor out common build rules for building variations of binaries
* Add a gtest for imgdiag

Bug: 17611661
Change-Id: I3ac852a0d223af66f6d59ae5dbc3df101475e3d0