Add lint-makefiles Makefile linting test.

We add a 'make check' test that lints all Makefiles in the source
directory of the glibc build. This linting test ensures that the
lines in all Makefiles will be sorted correctly as developers
creates patches.  It is added to 'make check' because it is
light-weight and supports the existing developer workflow

The test adds ~3s to a 'make check' execution.

No regressions on x86_64 and i686.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Makefile

@@ -564,6 +564,16 @@ $(objpfx)check-wrapper-headers.out: scripts/check-wrapper-headers.py $(headers)
 	  --generated $(common-generated) > $@; $(evaluate-test)
 endif # $(headers)
 
+# Lint all Makefiles; including this one.  Pass `pwd` as the source
+# directory since the top-level Makefile is in the root of the source
+# tree and these tests are run from there.  We add light-weight linting
+# to the 'check' target to support the existing developer workflow of:
+# edit -> make -> make check; without needing an additional step.
+tests-special += $(objpfx)lint-makefiles.out
+$(objpfx)lint-makefiles.out: scripts/lint-makefiles.sh
+	$(SHELL) $< "$(PYTHON)" `pwd` > $@ ; \
+	$(evaluate-test)
+
 define summarize-tests
 @grep -E -v '^(PASS|XFAIL):' $(objpfx)$1 || true
 @echo "Summary of test results$2:"

scripts/lint-makefiles.sh

@@ -0,0 +1,74 @@
+#!/bin/bash
+# Copyright (C) 2023 Free Software Foundation, Inc.
+# This file is part of the GNU C Library.
+
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <https://www.gnu.org/licenses/>.
+
+# This script checks to see that all Makefiles in the source tree
+# conform to the sorted variable rules as defined by:
+# scripts/sort-makefile-lines.py.
+# Any difference is an error and should be corrected e.g. the lines
+# reordered to sort correctly.
+# The intent with this check is to ensure that changes made by
+# developers match the expected format for the project.
+
+export LC_ALL=C
+
+tmpfile="$(mktemp)"
+
+cleanup () {
+  rm -f -- "$tmpfile"
+}
+
+trap cleanup 0
+
+PYTHON=$1
+# Absolute or relative path to the source directory.
+srcdir=$2
+
+# Must specify $PYTHON.
+if [ -z "$PYTHON" ]; then
+  echo 'Please specify $PYTHON interpreter'
+  exit 1
+fi
+# Absolute or relative $srcdir must exist and be a directory.
+if [ ! -d "$srcdir" ]; then
+  echo 'Please specify $srcdir in which to look for Makefiles'
+  exit 1
+fi
+
+linted=0
+failed=0
+for mfile in `find "$srcdir" -name Makefile`; do
+    $PYTHON "${srcdir}/scripts/sort-makefile-lines.py" < "$mfile" > "$tmpfile"
+    # Printed the expected -> actual difference on error.
+    if ! diff -u --label "$mfile.expected" "$tmpfile" "$mfile"; then
+        failed=$((failed+1))
+    fi
+    linted=$((linted+1))
+done
+# Must have linted at least the top-level Makefile.
+if [ $linted -lt 1 ]; then
+  echo "Did not lint any Makefiles!"
+  exit 1
+fi
+if [ $failed -gt 0 ]; then
+  echo "---"
+  echo "Tested $linted Makefiles and $failed were incorrectly sorted"
+  echo 'Please use `patch -R -pN` and the output above to correct the sorting'
+  exit 1
+fi
+# All Makefiles linted clean.
+exit 0