build: Move guix time machine to prelude

This deduplicates some code, and enforces consistency of the time
machine configuration between scripts.

contrib/guix/guix-build

@@ -234,21 +234,6 @@ host_to_commonname() {
 # Determine the reference time used for determinism (overridable by environment)
 SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:-$(git -c log.showSignature=false log --format=%at -1)}"
 
-# Execute "$@" in a pinned, possibly older version of Guix, for reproducibility
-# across time.
-time-machine() {
-    # shellcheck disable=SC2086
-    guix time-machine --url=https://git.savannah.gnu.org/git/guix.git \
-                      --commit=ae03f401381e956c4c41b4cf495cbde964fa43d0 \
-                      --cores="$JOBS" \
-                      --keep-failed \
-                      --fallback \
-                      ${SUBSTITUTE_URLS:+--substitute-urls="$SUBSTITUTE_URLS"} \
-                      ${ADDITIONAL_GUIX_COMMON_FLAGS} ${ADDITIONAL_GUIX_TIMEMACHINE_FLAGS} \
-                      -- "$@"
-}
-
-
 # Precious directories are those which should not be cleaned between successive
 # guix builds
 depends_precious_dir_names='SOURCES_PATH BASE_CACHE SDK_PATH'

contrib/guix/guix-codesign

@@ -222,20 +222,6 @@ JOBS="${JOBS:-$(nproc)}"
 # Determine the reference time used for determinism (overridable by environment)
 SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:-$(git -c log.showSignature=false log --format=%at -1)}"
 
-# Execute "$@" in a pinned, possibly older version of Guix, for reproducibility
-# across time.
-time-machine() {
-    # shellcheck disable=SC2086
-    guix time-machine --url=https://git.savannah.gnu.org/git/guix.git \
-                      --commit=ae03f401381e956c4c41b4cf495cbde964fa43d0 \
-                      --cores="$JOBS" \
-                      --keep-failed \
-                      --fallback \
-                      ${SUBSTITUTE_URLS:+--substitute-urls="$SUBSTITUTE_URLS"} \
-                      ${ADDITIONAL_GUIX_COMMON_FLAGS} ${ADDITIONAL_GUIX_TIMEMACHINE_FLAGS} \
-                      -- "$@"
-}
-
 # Make sure an output directory exists for our builds
 OUTDIR_BASE="${OUTDIR_BASE:-${VERSION_BASE}/output}"
 mkdir -p "$OUTDIR_BASE"

contrib/guix/libexec/prelude.bash

@@ -45,6 +45,22 @@ EOF
 exit 1
 fi
 
+################
+# Execute "$@" in a pinned, possibly older version of Guix, for reproducibility
+# across time.
+time-machine() {
+    # shellcheck disable=SC2086
+    guix time-machine --url=https://git.savannah.gnu.org/git/guix.git \
+                      --commit=ae03f401381e956c4c41b4cf495cbde964fa43d0 \
+                      --cores="$JOBS" \
+                      --keep-failed \
+                      --fallback \
+                      ${SUBSTITUTE_URLS:+--substitute-urls="$SUBSTITUTE_URLS"} \
+                      ${ADDITIONAL_GUIX_COMMON_FLAGS} ${ADDITIONAL_GUIX_TIMEMACHINE_FLAGS} \
+                      -- "$@"
+}
+
+
 ################
 # Set common variables
 ################