[tools] Add always_optimize option for drake_cc_library

[jwnimmer-tri]

Use it in our low-level OBB code.

Motivated by #22370. In that instance, this brings one test case out of a larger test program down from 11.0 seconds to 3.4 seconds of wall time.

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This change is 

[jwnimmer-tri]

+@rpoyner-tri and +@sherm1 and +@xuchenhan-tri design feedback, please.

Sometimes in our Debug builds our higher-layer test programs are astonishingly slow. Here we see it with OBB but we've also see in with RotationMatrix and RigidTransform. I think for inner-loop, low-level libraries we should probably not use O0 by default, since it is such a penalty.

What do you think about this idea?

We could fiddle with the flags a little bit, maybe keep DRAKE_ASSERT turned on but eigen assertions turned off? Or keep it de-optimized during its local unit test, but optimized when used outside of the package?

Mostly looking for the kind of UX concepts we want here for our developers (and CI).

[rpoyner-tri]

I like this. It may not solve all the things, but it's easy to at least experiment with.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: LGTM missing from assignees rpoyner-tri(platform),sherm1(platform),xuchenhan-tri(platform)

[xuchenhan-tri]

Looks good to me in general. I like keeping the DRAKE_ASSERT on, but I’m not sure how much it eats into the gain? Another thing that’s worth discussing here is what’s our policy for allowing turning the flag on.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: LGTM missing from assignees rpoyner-tri(platform),sherm1(platform),xuchenhan-tri(platform)

[sherm1]

As written (-DNDEBUG) all the asserts are disarmed. I suspect that's necessary to achieve enough performance gain -- I'm thinking about the many super-expensive DRAKE_ASSERT_VOIDs we have at low levels that run eigenvalue checks and the like.

This option makes sense to me for CI where some Debug tests are excessively time consuming. In a Debug workflow during development though it would be nice to be able to conveniently turn it off. Could we have a --debug_everything build flag that would override?

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: LGTM missing from assignees rpoyner-tri(platform),sherm1(platform),xuchenhan-tri(platform)