jolt build: compile an app to a standalone binary (Phase 4 stages 1-2)

Restores the standalone-binary capability the Janet host had. `bin/joltc build
-m NS -o OUT` AOT-compiles an app into a single self-contained executable — the
whole runtime, clojure.core, stdlib and compiler embedded, no Chez install or
jolt source needed at runtime.

Pipeline (host/chez/build.ss, host primitive jolt.host/build-binary driven by
jolt.main's build command): resolve deps, load the entry namespace recording the
app namespaces in dependency order, re-emit each to Scheme, textually inline the
cli.ss runtime load sequence into one flat source + the app + a launcher, then
compile-file -> make-boot-file -> embed the boot as C bytes -> cc-link against
libkernel.a.

Two non-obvious bits: the compile pass runs in a fresh Chez, not the loaded
runtime (regex.ss shadows top-level `error`, which otherwise bakes a broken
reference into the boot); and the launcher installs scheme-start rather than
running -main at top level, since boot top-level forms execute during heap build
before argv is set, so args only reach -main through scheme-start.

Loader: a require of an in-memory namespace with no source file now no-ops, so
AOT'd app namespaces satisfy require in a built binary.

Mode flags (--opt/--dev, default release) are plumbed; the optimization passes
they gate come in a later stage. RFC 0007 has the design. Gated by `make
buildsmoke`.

host/chez/cli.ss

@@ -66,6 +66,11 @@
          (display result) (newline))))
     ;; otherwise dispatch the argv through jolt.main/-main
     (else
+     ;; `build` AOT-compiles an app to a standalone binary — load the build
+     ;; driver (the cross-compiler emitter) on demand so a normal run never pays
+     ;; for it. It defines jolt.host/build-binary, which jolt.main's build cmd calls.
+     (when (and (pair? cli-args) (string=? (car cli-args) "build"))
+       (load "host/chez/build.ss"))
      (load-namespace "jolt.main")
      (let ((mainv (var-deref "jolt.main" "-main")))
        (apply jolt-invoke mainv cli-args)))))