gnu: nsis: Respect SOURCE-DATE-EPOCH for reproducibility

* gnu/packages/patches/nsis-source-date-epoch.patch: New patch.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/installers.scm (make-nsis)[source]: Apply it.

gnu/local.mk

@@ -1468,6 +1468,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/network-manager-plugin-path.patch	\
   %D%/packages/patches/nginx-socket-cloexec.patch		\
   %D%/packages/patches/nsis-env-passthru.patch			\
+  %D%/packages/patches/nsis-source-date-epoch.patch		\
   %D%/packages/patches/nss-increase-test-timeout.patch		\
   %D%/packages/patches/nss-3.56-pkgconfig.patch			\
   %D%/packages/patches/ntfs-3g-CVE-2019-9755.patch		\

gnu/packages/installers.scm

@@ -42,7 +42,8 @@ (define (make-nsis machine target-arch nsis-target-type)
                 (sha256
                  (base32
                   "1sbwx5vzpddharkb7nj4q5z3i5fbg4lan63ng738cw4hmc4v7qdn"))
-                (patches (search-patches "nsis-env-passthru.patch"))))
+                (patches (search-patches "nsis-env-passthru.patch"
+                                         "nsis-source-date-epoch.patch"))))
       (build-system scons-build-system)
       (native-inputs `(("xgcc" ,xgcc)
                        ("xbinutils" ,xbinutils)

gnu/packages/patches/nsis-source-date-epoch.patch

@@ -0,0 +1,23 @@
+Honour SOURCE_DATE_EPOCH for VERSION default
+
+Merged upstream as cd3f1024a37a332f1d4fa96a817ca80dfa2a478c, but not yet in a
+release. GitHub PR: https://github.com/kichik/nsis/pull/13
+
+Python snippet from: https://reproducible-builds.org/docs/source-date-epoch/#python
+
+
+diff --git a/SConstruct b/SConstruct
+index e8252c9..41786f2 100755
+--- a/SConstruct
++++ b/SConstruct
+@@ -95,8 +95,8 @@ default_doctype = 'html'
+ if defenv.WhereIs('hhc', os.environ['PATH']):
+ 	default_doctype = 'chm'
+ 
+-from time import strftime, gmtime
+-cvs_version = strftime('%d-%b-%Y.cvs', gmtime())
++import time
++cvs_version = time.strftime('%d-%b-%Y.cvs', time.gmtime(int(os.environ.get('SOURCE_DATE_EPOCH', time.time()))))
+ 
+ opts = Variables()
+