makefile: fix build with overriden UTILS

The make build was failing when the list of UTILS didn't contain stdbuf.
This fixes this issue by adding feat_externa_libstdbuf only when stdbuf is being compiled.

Fixes #8701

Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>

Author: Ecordonnier

.github/workflows/CICD.yml

@@ -341,6 +341,12 @@ jobs:
         ! test -f /tmp/usr/local/share/zsh/site-functions/_install
         ! test -f /tmp/usr/local/share/bash-completion/completions/head
         ! test -f /tmp/usr/local/share/fish/vendor_completions.d/cat.fish
+    - name: "`make with UTILS overridden`"
+      shell: bash
+      run: |
+        set -x
+        # Regression-test for https://github.com/uutils/coreutils/issues/8701
+        make UTILS="rm chmod chown chgrp mv du"
 
   build_rust_stable:
     name: Build/stable

GNUmakefile

@@ -202,12 +202,15 @@ ifneq ($(OS),Windows_NT)
 	PROGS := $(PROGS) $(UNIX_PROGS)
 # Build the selinux command even if not on the system
 	PROGS := $(PROGS) $(SELINUX_PROGS)
-# Always use external libstdbuf when building with make (Unix only)
-	CARGOFLAGS += --features feat_external_libstdbuf
 endif
 
 UTILS ?= $(PROGS)
 
+ifneq ($(findstring stdbuf,$(UTILS)),)
+    # Use external libstdbuf per default. It is more robust than embedding libstdbuf.
+	CARGOFLAGS += --features feat_external_libstdbuf
+endif
+
 # Programs with usable tests
 TEST_PROGS  := \
 	base32 \