guix: strip binaries in libexec

31679 moved some internal binaries to libexec/, but the Guix build
wasn't updated to stip these binaries of their debug symbols.

contrib/guix/libexec/build.sh

@@ -290,7 +290,7 @@ mkdir -p "$DISTSRC"
             *)
                 # Split binaries from their debug symbols
                 {
-                    find "${DISTNAME}/bin" -type f -executable -print0
+                    find "${DISTNAME}/bin" "${DISTNAME}/libexec" -type f -executable -print0
                 } | xargs -0 -P"$JOBS" -I{} "${DISTSRC}/build/split-debug.sh" {} {} {}.dbg
                 ;;
         esac