Revert "guix: remove errant leftover from #29648"

This reverts commit fd8527a20e (#29787)

contrib/guix/libexec/build.sh

@@ -310,6 +310,12 @@ mkdir -p "$DISTSRC"
     (
         cd installed
 
+        case "$HOST" in
+            *mingw*)
+                mv --target-directory="$DISTNAME"/lib/ "$DISTNAME"/bin/*.dll
+                ;;
+        esac
+
         # Prune libtool and object archives
         find . -name "lib*.la" -delete
         find . -name "lib*.a" -delete
@@ -323,6 +329,7 @@ mkdir -p "$DISTSRC"
                 # Split binaries and libraries from their debug symbols
                 {
                     find "${DISTNAME}/bin" -type f -executable -print0
+                    find "${DISTNAME}/lib" -type f -print0
                 } | xargs -0 -P"$JOBS" -I{} "${DISTSRC}/contrib/devtools/split-debug.sh" {} {} {}.dbg
                 ;;
         esac