guix, refactor: Move `distsrc_for_host()` to `prelude.bash`

diff --git a/contrib/guix/guix-build b/contrib/guix/guix-build
index a02c3603..eed9d459 100755
--- a/contrib/guix/guix-build
+++ b/contrib/guix/guix-build
@@ -85,14 +85,6 @@ export HOSTS="${HOSTS:-x86_64-linux-gnu arm-linux-gnueabihf aarch64-linux-gnu ri
                        x86_64-w64-mingw32
                        x86_64-apple-darwin arm64-apple-darwin}"
 
-# Usage: distsrc_for_host HOST
-#
-#   HOST: The current platform triple we're building for
-#
-distsrc_for_host() {
-    echo "${DISTSRC_BASE}/distsrc-${VERSION}-${1}"
-}
-
 # Accumulate a list of build directories that already exist...
 hosts_distsrc_exists=""
 for host in $HOSTS; do
diff --git a/contrib/guix/guix-codesign b/contrib/guix/guix-codesign
index f985fd4c..1ceb65d6 100755
--- a/contrib/guix/guix-codesign
+++ b/contrib/guix/guix-codesign
@@ -99,18 +99,10 @@ fi
 # Default to building for all supported HOSTs (overridable by environment)
 export HOSTS="${HOSTS:-x86_64-w64-mingw32 x86_64-apple-darwin arm64-apple-darwin}"
 
-# Usage: distsrc_for_host HOST
-#
-#   HOST: The current platform triple we're building for
-#
-distsrc_for_host() {
-    echo "${DISTSRC_BASE}/distsrc-${VERSION}-${1}-codesigned"
-}
-
 # Accumulate a list of build directories that already exist...
 hosts_distsrc_exists=""
 for host in $HOSTS; do
-    if [ -e "$(distsrc_for_host "$host")" ]; then
+    if [ -e "$(distsrc_for_host "$host" codesigned)" ]; then
         hosts_distsrc_exists+=" ${host}"
     fi
 done
@@ -134,7 +126,7 @@ packages cache, the garbage collector roots for Guix environments, and the
 output directory.
 EOF
 for host in $hosts_distsrc_exists; do
-    echo "     ${host} '$(distsrc_for_host "$host")'"
+    echo "     ${host} '$(distsrc_for_host "$host" codesigned)'"
 done
 exit 1
 else
@@ -263,8 +255,8 @@ INFO: Codesigning ${VERSION:?not set} for platform triple ${HOST:?not set}:
       ...using reference timestamp: ${SOURCE_DATE_EPOCH:?not set}
       ...from worktree directory: '${PWD}'
           ...bind-mounted in container to: '/bitcoin'
-      ...in build directory: '$(distsrc_for_host "$HOST")'
-          ...bind-mounted in container to: '$(DISTSRC_BASE=/distsrc-base && distsrc_for_host "$HOST")'
+      ...in build directory: '$(distsrc_for_host "$HOST" codesigned)'
+          ...bind-mounted in container to: '$(DISTSRC_BASE=/distsrc-base && distsrc_for_host "$HOST" codesigned)'
       ...outputting in: '$(outdir_for_host "$HOST" codesigned)'
           ...bind-mounted in container to: '$(OUTDIR_BASE=/outdir-base && outdir_for_host "$HOST" codesigned)'
       ...using detached signatures in: '${DETACHED_SIGS_REPO:?not set}'
@@ -347,7 +339,7 @@ EOF
                                         JOBS="$JOBS" \
                                         SOURCE_DATE_EPOCH="${SOURCE_DATE_EPOCH:?unable to determine value}" \
                                         ${V:+V=1} \
-                                        DISTSRC="$(DISTSRC_BASE=/distsrc-base && distsrc_for_host "$HOST")" \
+                                        DISTSRC="$(DISTSRC_BASE=/distsrc-base && distsrc_for_host "$HOST" codesigned)" \
                                         OUTDIR="$(OUTDIR_BASE=/outdir-base && outdir_for_host "$HOST" codesigned)" \
                                         DIST_ARCHIVE_BASE=/outdir-base/dist-archive \
                                         DETACHED_SIGS_REPO=/detached-sigs \
diff --git a/contrib/guix/libexec/prelude.bash b/contrib/guix/libexec/prelude.bash
index c13f24c5..21e668cf 100644
--- a/contrib/guix/libexec/prelude.bash
+++ b/contrib/guix/libexec/prelude.bash
@@ -80,6 +80,15 @@ time-machine() {
                       -- "$@"
 }
 
+# Usage: distsrc_for_host HOST [SUFFIX]
+#
+#   HOST: The current platform triple we're building for
+#   SUFFIX: Optional. If provided, appended to the directory name as "-SUFFIX"
+#
+distsrc_for_host() {
+    echo "${DISTSRC_BASE}/distsrc-${VERSION}-${1}${2:+-${2}}"
+}
+
 # Usage: outdir_for_host HOST [SUFFIX]
 #
 #   HOST: The current platform triple we're building for