add --xpatch flag to the boot{quick} command target

The `--xpatch` flag explicitly requests that an "xpatch" is created in
the "xc-..." directory. The file is created anyway, currently, but
`--xpatch` is meant to make it more official.

Original commit: racket/ChezScheme@288ad38

build.zuo

@@ -103,8 +103,13 @@
 
   ;; besides `<machine>` argument, accepts `--host-scheme <command>`
   ;; or `--host-workarea <dir>", and recognizes `SCHEME=...` if neither
-  ;; flag is provided
-  (define (parse-boot-args args k)
+  ;; flag is provided; also recognizes "--xpatch" before anything else
+  ;; to request that "xpatch" is left in an "xc-" directory
+  (define (parse-boot-args orig-args k)
+    (define xpatch?
+      (and (pair? orig-args)
+           (equal? "--xpatch" (car orig-args))))
+    (define args (if xpatch? (cdr orig-args) orig-args))
     (define host-scheme-via-flag
       (and (pair? args)
            (equal? (car args) "--host-scheme")
@@ -132,19 +137,19 @@
     (define host-m (if host-scheme
                        (ask-scheme-machine host-scheme)
                        m))
-    (k xm host-m host-scheme host-workarea))
+    (k xm host-m host-scheme host-workarea xpatch?))
 
   ;; Cross-builds for a machine type that is specified as an argument;
   ;; the machine type defaults to the `defaultm` configuration entry, and
   ;; that default is normally useful if the current machine type is "pb"
   (define (cross-build-boot token args ccopts make-targets record-dep?)
     (parse-boot-args
      args
-     (lambda (xm m host-scheme host-workarea)
+     (lambda (xm m host-scheme host-workarea xpatch?)
        (unless (or host-scheme host-workarea)
          (check-not-kernel-only))
        (alert (~a "building boot files for " xm " using " m))
-       (boot:cross-build-boot token ccopts make-targets
+       (boot:cross-build-boot token ccopts make-targets xpatch?
                               xm host-scheme host-workarea
                               at-dir config vars m)
        ;; record success so boot files will not be rebuilt from pb
@@ -157,15 +162,18 @@
   (define (cross-reboot token args)
     (parse-boot-args
      args
-     (lambda (xm m host-scheme host-workarea)
+     (lambda (xm m host-scheme host-workarea xpatch?)
+       (when xpatch? (error "cannot generate xpatch in reboot mode"))
        (define scheme (or host-scheme
                           (build-path host-workarea m "bin" m (.exe "scheme"))))
        (define options (if host-workarea
                            (hash 'env
                                  (cons "SCHEMEHEAPDIRS"
                                        (path->complete-path (build-path host-workarea "boot" m))))
                            (hash)))
-       (reboot m xm scheme (hash 'shell-options options 'out-dir (at-dir ".."))))))
+       (reboot m xm scheme (hash 'shell-options options
+                                 'out-dir (at-dir "..")
+                                 'work-dir (at-dir ".."))))))
 
   ;; used to create a target for "quickboot", or just record dependency for other modes
   ;; of building boot files
@@ -313,7 +321,7 @@
                    (check-not-kernel-only)
                    (parse-boot-args
                     args
-                    (lambda (xm m host-scheme host-workarea)
+                    (lambda (xm m host-scheme host-workarea xpatch?)
                       (unless (or host-scheme host-workarea)
                         (build/dep (find-target "kernel" the-targets) token))
                       (build-boot-target

makefiles/boot.zuo

@@ -30,7 +30,7 @@
 ;; Cross-builds for a machine type that is specified as an argument;
 ;; the machine type defaults to the `defaultm` configuration entry, and
 ;; that default is normally useful if the current machine type is "pb"
-(define (cross-build-boot token ccopts make-targets
+(define (cross-build-boot token ccopts make-targets xpatch?
                           xm host-scheme host-workarea
                           at-dir config vars m)
   (define dir (at-dir ".." (~a "xc-" xm)))
@@ -58,7 +58,9 @@
     (build (find-target "clean" targets) token)
     (map (lambda (t)
            (build (find-target t targets) token))
-         make-targets))
+         make-targets)
+    (when xpatch?
+      (build (find-target (build-path s-dir "xpatch") targets) token)))
   (define boot-xm-dir (at-dir "../boot" xm))
   (mkdir-p boot-xm-dir)
   (for-each (lambda (file)