fix: trace embedded Chez boot stages

ober

81cb59081bd1348a30206645366f554f6e0c311d

diff --git a/support/multicall-main.c b/support/multicall-main.c
index 60a00da..42118b3 100644
--- a/support/multicall-main.c
+++ b/support/multicall-main.c
@@ -98,6 +98,12 @@ static void call_scheme_1(const char *who, ptr arg) {
     Scall1(procedure, arg);
 }
 
+static void debug_boot_stage(const char *stage) {
+    if (getenv("JERBOA_DEBUG_BOOT") != NULL) {
+        fprintf(stderr, "jerboa: boot %s\n", stage);
+    }
+}
+
 /* ── jerbuild lib bundle: extracted to a per-sha cache dir on demand ───────
  * Layout: $XDG_CACHE_HOME/jerbuild/<sha256>/ (or ~/.cache/jerbuild/<sha256>/)
  * holding the Jerboa stdlib + Chez kernel files the `jerbuild binary`/`build`
@@ -644,10 +650,14 @@ int main(int argc, const char *argv[]) {
      * to native .wpo (cross-built .wpo carry the build host's machine-type). */
     if (!strcmp(name, "jerboa") && argc > 1 && !strcmp(argv[1], "runtime")) {
         jerboa_maybe_enable_shadow_stack("jerboa");
+        debug_boot_stage("scheme_init");
         Sscheme_init(NULL);
+        debug_boot_stage("register_boot_files");
         Sregister_boot_file_bytes("petite", (void *)petite_boot_data, petite_boot_size);
         Sregister_boot_file_bytes("scheme", (void *)scheme_boot_data, scheme_boot_size);
+        debug_boot_stage("build_heap");
         Sbuild_heap(NULL, register_symbols);
+        debug_boot_stage("configure_library_paths");
         configure_embedded_library_paths();
         int st = (argc > 2) ? Sscheme_script(argv[2], argc - 2, argv + 2)
                             : Sscheme_start(argc - 1, argv + 1);
@@ -682,10 +692,14 @@ int main(int argc, const char *argv[]) {
     setenv("JERBOA_MULTICALL_NAME", mode, 1);
 
     jerboa_maybe_enable_shadow_stack(mode);
+    debug_boot_stage("scheme_init");
     Sscheme_init(NULL);
+    debug_boot_stage("register_boot_files");
     Sregister_boot_file_bytes("petite", (void *)petite_boot_data, petite_boot_size);
     Sregister_boot_file_bytes("scheme", (void *)scheme_boot_data, scheme_boot_size);
+    debug_boot_stage("build_heap");
     Sbuild_heap(NULL, register_symbols);
+    debug_boot_stage("configure_library_paths");
     configure_embedded_library_paths();
 
     const char *prog = write_program_tmpfile();