depend-cleanup: Add verbose (-v) and pretend/dry-run (-n) flags

[jrtc27]

Summary

These are useful for testing new additions to the script. Whilst here,
harden the script a little and improve error messages.

[imp]

Conditional on rebasing to something newer :)

[jrtc27]

Rebase

[jrtc27]

Handle MACHINE_ARCH being empty during bootstrap-tools use

[imp]

In D31007#932469, @jrtc27 wrote:

Handle MACHINE_ARCH being empty during bootstrap-tools use

When can it be empty?

[jrtc27]

In D31007#932472, @imp wrote:

In D31007#932469, @jrtc27 wrote:

Handle MACHINE_ARCH being empty during bootstrap-tools use

When can it be empty?

We run the script twice. The first time is during bootstrap-tools for obj-tools and there it's under BMAKE(ENV) which doesn't do any TARGET/MACHINE(_ARCH) assignment (just leaves them as they are for the parent, which may mean re-inferring). The second time is the one for the real OBJTOP where it's run under WMAKE(ENV) and picks up TARGET(_ARCH)=MACHINE(_ARCH) from CROSSENV.

Probably _cleanobj_fast_depend_hack should just do env MACHINE=${MACHINE} MACHINE_ARCH=${MACHINE_ARCH} instead, to be honest.

[jrtc27]

Rebase atop D40968