gnu: ghostscript: Make "/CreationDate", "/ModDate" optional, depending on environment variable.

* gnu/packages/patches/ghostscript-no-header-creationdate.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/ghostscript.scm (ghostscript): Use it.

gnu/local.mk

@@ -621,6 +621,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/ghostscript-CVE-2017-8291.patch		\
   %D%/packages/patches/ghostscript-no-header-id.patch		\
   %D%/packages/patches/ghostscript-no-header-uuid.patch		\
+  %D%/packages/patches/ghostscript-no-header-creationdate.patch \
   %D%/packages/patches/ghostscript-runpath.patch		\
   %D%/packages/patches/glib-networking-ssl-cert-file.patch	\
   %D%/packages/patches/glib-tests-timer.patch			\

gnu/packages/ghostscript.scm

@@ -144,6 +144,7 @@ printing, and psresize, for adjusting page sizes.")
           "0lyhjcrkmd5fcmh8h56bs4xr9k4jasmikv5vsix1hd4ai0ad1q9b"))
         (patches (search-patches "ghostscript-runpath.patch"
                                  "ghostscript-CVE-2017-8291.patch"
+                                 "ghostscript-no-header-creationdate.patch"
                                  "ghostscript-no-header-id.patch"
                                  "ghostscript-no-header-uuid.patch"))
         (modules '((guix build utils)))
@@ -154,14 +155,7 @@ printing, and psresize, for adjusting page sizes.")
          '(begin
             (for-each delete-file-recursively '("freetype" "jbig2dec" "jpeg"
                                                 "lcms2" "libpng"
-                                                "tiff" "zlib"))
-            ;; Get rid of timestamps (remove /CreationDate and /ModDate).
-            (substitute* "devices/vector/gdevpdf.c"
-             ((", but we do the same")
-              (string-append "*/ "
-                             "if (!getenv(\"GS_GENERATE_UUIDS\") || "
-                             "(strcmp(getenv(\"GS_GENERATE_UUIDS\"), \"0\") != 0 && "
-                             "strcmp(getenv(\"GS_GENERATE_UUIDS\"), \"no\") != 0)) /*")))))))
+                                                "tiff" "zlib"))))))
     (build-system gnu-build-system)
     (outputs '("out" "doc"))                  ;19 MiB of HTML/PS doc + examples
     (arguments

gnu/packages/patches/ghostscript-no-header-creationdate.patch

@@ -0,0 +1,22 @@
+This patch makes emission of /CreationDate and /ModDate headers optional.
+
+If the environment variable GS_GENERATE_UUIDS is set to "0" or "no", it will
+not write out the "/ID" field (if that's permissible).
+
+Upstream does not want to do this.
+
+See: https://bugs.ghostscript.com/show_bug.cgi?id=698208
+diff --git a/orig/gnu-ghostscript-9.14.0/devices/vector/gdevpdf.c b/bb/gnu-ghostscript-9.14.0/devices/vector/gdevpdf.c
+index 0fb067e..b342e2c 100644
+--- orig/gnu-ghostscript-9.14.0/devices/vector/gdevpdf.c
++++ gnu-ghostscript-9.14.0/devices/vector/gdevpdf.c
+@@ -305,6 +305,9 @@ pdf_initialize_ids(gx_device_pdf * pdev)
+      * date and time, rather than (for example) %%CreationDate from the
+      * PostScript file.  We think this is wrong, but we do the same.
+      */
++    if (!getenv("GS_GENERATE_UUIDS") ||
++        (strcasecmp(getenv("GS_GENERATE_UUIDS"), "0") != 0 &&
++         strcasecmp(getenv("GS_GENERATE_UUIDS"), "no") != 0))
+     {
+         struct tm tms;
+         time_t t;