New 00-syntax tier loaded FIRST (before 00-kernel), interpreted defmacros, so the
control macros the compiler and every later tier depend on can live in Clojure.
Validated by moving when: the kernel tier, self-hosted analyzer and seq/coll
tiers all compile against the overlay when. Constraint: syntax-tier macros may use
only special forms + core-renames seed primitives (not second/peek/kernel fns).
conformance 228/228 x3, full suite green.
