Avoid depending on 'git' to gather the commit id

src/CHANGELOG

@@ -215,6 +215,9 @@ ECL 11.1.2
    is done to avoid accidentally generating header files with the same name
    as those in the C library. Take for instance, float.lsp -> float.h.
 
+ - ECL no longer relies on "git" being installed to gather the git commit id
+   and setting (ext:lisp-implementation-vcs-id).
+
 ;;; Local Variables: ***
 ;;; mode:text ***
 ;;; fill-column:79 ***

src/bare.lsp.in

@@ -166,13 +166,9 @@
 ;;; * Update version number now that SI:SYSTEM is available
 ;;;
 
-(when (and (not (member :windows *features*))
-           (probe-file "@top_srcdir@/../.git/"))
-  (when (probe-file "COMMIT-ID")
-    (delete-file "COMMIT-ID"))
-  (when (and (zerop (si::system "(cd \"@top_srcdir@\" && git log --format=oneline -1) > COMMIT-ID"))
-             (probe-file "COMMIT-ID"))
-    (let* ((file (open "COMMIT-ID" :direction :input :element-type :default
+(let ((commit-id (probe-file "@top_srcdir@/../.git/ORIG_HEAD")))
+  (when commit-id
+    (let* ((file (open commit-id :direction :input :element-type :default
                        :external-format :default))
            (line (read-line file))
            (l (length line)))