guix: Make x86_64-w64-mingw32 builds reproducible

- Add "--no-insert-timestamp" LDFLAG for x86_64-w64-mingw32 builds

"The option --no-insert-timestamp can be used to insert a zero value for
the timestamp, this ensuring that binaries produced from identical
sources will compare identically." - ld(1)

- Set "SetDateSave off" in NSIS script

From https://nsis.sourceforge.io/Docs/Chapter4.html#flags

"This command sets the file date/time saving flag which is used by the
File command to determine whether or not to save the last write date and
time of the file, so that it can be restored on installation. Valid
flags are 'on' and 'off'. 'on' is the default."

- Add commented out NSIS options for reproducibility debugging in NSIS
  script

- Make ZIPs deterministic by reseting file modification times to
  SOURCE_DATE_EPOCH using touch(1) (Reference:
  https://reproducible-builds.org/docs/archives/)

contrib/guix/libexec/build.sh

@@ -178,6 +178,7 @@ HOST_CXXFLAGS="$HOST_CFLAGS"
 # LDFLAGS
 case "$HOST" in
     *linux*)  HOST_LDFLAGS="-Wl,--as-needed -Wl,--dynamic-linker=$glibc_dynamic_linker -static-libstdc++" ;;
+    *mingw*)  HOST_LDFLAGS="-Wl,--no-insert-timestamp" ;;
 esac
 
 # Make $HOST-specific native binaries from depends available in $PATH
@@ -271,10 +272,14 @@ export PATH="${BASEPREFIX}/${HOST}/native/bin:${PATH}"
         # for release
         case "$HOST" in
             *mingw*)
+                find "${DISTNAME}" -not -name "*.dbg" -print0 \
+                    | xargs -0r touch --no-dereference --date="@${SOURCE_DATE_EPOCH}"
                 find "${DISTNAME}" -not -name "*.dbg" \
                     | sort \
                     | zip -X@ "${OUTDIR}/${DISTNAME}-${HOST//x86_64-w64-mingw32/win64}.zip" \
                     || ( rm -f "${OUTDIR}/${DISTNAME}-${HOST//x86_64-w64-mingw32/win64}.zip" && exit 1 )
+                find "${DISTNAME}" -name "*.dbg" -print0 \
+                    | xargs -0r touch --no-dereference --date="@${SOURCE_DATE_EPOCH}"
                 find "${DISTNAME}" -name "*.dbg" \
                     | sort \
                     | zip -X@ "${OUTDIR}/${DISTNAME}-${HOST//x86_64-w64-mingw32/win64}-debug.zip" \

share/setup.nsi.in

@@ -2,6 +2,11 @@ Name "@PACKAGE_NAME@ (64-bit)"
 
 RequestExecutionLevel highest
 SetCompressor /SOLID lzma
+SetDateSave off
+
+# Uncomment these lines when investigating reproducibility errors
+#SetCompress off
+#SetDatablockOptimize off
 
 # General Symbol Definitions
 !define REGKEY "SOFTWARE\$(^Name)"