* libguile/goops.h (SCM_VTABLE_FLAG_GOOPS_STATIC): Reserve the fourth
GOOPS flag to indicate that a class has static slot allocation.
* libguile/goops.c (scm_init_goops_builtins): Define
vtable-flag-goops-static for goops.scm.
* module/oop/goops.scm (class-has-statically-allocated-slots?): New
helper.
(build-slots-list): Instead of the ad-hoc checks for <class> or
<slot>, use the new helper.
(initialize): Accept #:static-slot-allocation? keyword.
* module/system/foreign-object.scm (make-foreign-object-type): Declare
foreign object classes as having static slot allocation.
* test-suite/tests/goops.test ("static slot allocation"): Add tests.
