Follow-up patch committed, after my use of the one-argument variant of static_assert() broke bootstrap on Solaris (sorry Rainer!).
The one-arg form is new since C23, while Solaris <assert.h> only supports the two-arg form (C11).

I have confirmed that other target libraries use the two-arg form, and bootstrapped the attached patch on x86_64-pc-linux-gnu.

FX