Resolve optional libc entries at runtime, not boot load

A literal (foreign-procedure "chmod" ...) in compiled code becomes a fasl
relocation resolved when the boot loads — on Windows (no chmod/sigemptyset/
sigaddset in the CRT) that killed joltc.exe before any guard could run
(msvcrt abort, exit 3). jolt-foreign-proc-safe defers the lookup through
eval at evaluation time, where the guard works and a missing entry just
yields the fallback. chmod also skips the /bin/sh fallback on nt (execute
is by extension).

host/chez/java/concurrency.ss

@@ -579,9 +579,9 @@
 ;; pthread_sigmask"). Guard so a non-POSIX host yields #f; jolt-set-sigint-blocked
 ;; then no-ops (Windows delivers ^C through the console, not a per-thread mask).
 (define c-pthread-sigmask
-  (guard (e (#t #f)) (foreign-procedure "pthread_sigmask" (int u8* u8*) int)))
-(define c-sigemptyset (guard (e (#t #f)) (foreign-procedure "sigemptyset" (u8*) int)))
-(define c-sigaddset (guard (e (#t #f)) (foreign-procedure "sigaddset" (u8* int) int)))
+  (jolt-foreign-proc-safe "pthread_sigmask" '(int u8* u8*) 'int))
+(define c-sigemptyset (jolt-foreign-proc-safe "sigemptyset" '(u8*) 'int))
+(define c-sigaddset (jolt-foreign-proc-safe "sigaddset" '(u8* int) 'int))
 ;; POSIX SIG_BLOCK/SIG_UNBLOCK numerics differ by platform: Linux/glibc 0/1,
 ;; Darwin/macOS 1/2 (SIG_UNBLOCK is SIG_BLOCK+1 on both). Resolve SIG_BLOCK for
 ;; this host from the machine-type symbol — macOS builds contain "osx".

host/chez/java/host-static-methods.ss

@@ -55,9 +55,7 @@
     (lambda ()
       (unless tried?
         (set! tried? #t)
-        (set! fp (guard (e (#t #f))
-                   (load-shared-object #f)
-                   (foreign-procedure "sched_yield" () int))))
+        (set! fp (jolt-foreign-proc-safe "sched_yield" '() 'int)))
       (if fp (fp) (sleep (make-time 'time-duration 0 0)))
       jolt-nil)))
 

host/chez/java/io.ss

@@ -80,13 +80,18 @@
 ;; every Chez binary) — no external toolchain. Falls back to /bin/sh chmod if the
 ;; symbol can't be resolved.
 (define jolt-chmod-755
-  (let ((c (guard (e (#t #f))
-             (load-shared-object #f)
-             (foreign-procedure "chmod" (string int) int))))
+  (let ((c (jolt-foreign-proc-safe "chmod" '(string int) 'int)))
     (lambda (path)
-      (if c
-          (c path #o755)
-          (system (string-append "chmod 755 '" path "'"))))))
+      (cond
+        (c (c path #o755))
+        ;; Windows has no chmod and needs none (execute is by extension)
+        ((let ((m (symbol->string (machine-type))))
+           (let loop ((i 0))
+             (cond ((> (+ i 2) (string-length m)) #f)
+                   ((string=? (substring m i (+ i 2)) "nt") #t)
+                   (else (loop (+ i 1))))))
+         0)
+        (else (system (string-append "chmod 755 '" path "'")))))))
 
 ;; A user-facing relative path resolves against JOLT_PWD — the user's cwd before
 ;; the launcher cd'd to the jolt repo root — matching the JVM, where io/file is

host/chez/rt.ss

@@ -11,6 +11,17 @@
 ;; Emitted programs do `(load "host/chez/rt.ss")`; this loads values.ss in turn.
 
 (load "host/chez/values.ss")
+;; Resolve a libc entry point at RUN time. A literal (foreign-procedure "name" …)
+;; in COMPILED code becomes a fasl relocation resolved when the boot loads — on a
+;; platform lacking the symbol (chmod/sigaddset on Windows) that kills the boot
+;; before any guard can run. eval defers the lookup to evaluation time, where the
+;; guard works; returns #f when the entry doesn't exist.
+(define (jolt-foreign-proc-safe name args res)
+  (guard (e (#t #f))
+    (load-shared-object #f)
+    (and (foreign-entry? name)
+         (eval `(foreign-procedure ,name ,args ,res)))))
+
 (load "host/chez/collections.ss")
 (load "host/chez/seq.ss")