* gnu/packages/patches/ghostscript-no-header-creationdate.patch: Disable
writing "xmp:ModifyDate" and "xmp:CreateDate" if GS_GENERATE_UUIDS is set to
"0" or "no".
* 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.