perlcheck: add script, run in CI, fix fallouts

Add script to run all Perl sources through `perl -c` to ensure no
issues, and run this script via GHA/checksrc in CI.

Fallouts:
- fix two repeated declarations.
- move `shell_quote()` from `testutil.pm` to `pathhelp.pm`, to
  avoid circular dependency in `globalconfig.pm`.

Closes #18745

scripts/Makefile.am

@@ -25,7 +25,8 @@
 EXTRA_DIST = coverage.sh completion.pl firefox-db2pem.sh checksrc.pl checksrc-all.pl \
   mk-ca-bundle.pl mk-unity.pl schemetable.c cd2nroff nroff2cd cdall cd2cd managen    \
   dmaketgz maketgz release-tools.sh verify-release cmakelint.sh mdlinkcheck          \
-  CMakeLists.txt pythonlint.sh randdisable wcurl top-complexity extract-unit-protos
+  CMakeLists.txt perlcheck.sh pythonlint.sh randdisable wcurl top-complexity         \
+  extract-unit-protos
 
 dist_bin_SCRIPTS = wcurl
 

scripts/perlcheck.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+#***************************************************************************
+#                                  _   _ ____  _
+#  Project                     ___| | | |  _ \| |
+#                             / __| | | | |_) | |
+#                            | (__| |_| |  _ <| |___
+#                             \___|\___/|_| \_\_____|
+#
+# Copyright (C) Dan Fandrich, <dan@coneharvesters.com>, Viktor Szakats, et al.
+#
+# This software is licensed as described in the file COPYING, which
+# you should have received as part of this distribution. The terms
+# are also available at https://curl.se/docs/copyright.html.
+#
+# You may opt to use, copy, modify, merge, publish, distribute and/or sell
+# copies of the Software, and permit persons to whom the Software is
+# furnished to do so, under the terms of the COPYING file.
+#
+# This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+# KIND, either express or implied.
+#
+# SPDX-License-Identifier: curl
+#
+###########################################################################
+
+# The xargs invocation is portable, but does not preserve spaces in file names.
+# If such a file is ever added, then this can be portably fixed by switching to
+# "xargs -I{}" and appending {} to the end of the xargs arguments (which will
+# call cmakelint once per file) or by using the GNU extension "xargs -d'\n'".
+
+set -eu
+
+cd "$(dirname "$0")"/..
+
+{
+  if [ -n "${1:-}" ]; then
+    for A in "$@"; do printf "%s\n" "$A"; done
+  elif git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
+    {
+      git ls-files | grep -E '\.(pl|pm)$'
+      git grep -l -E '^#!/usr/bin/env perl'
+    } | sort -u
+  else
+    # strip off the leading ./ to make the grep regexes work properly
+    find . -type f \( -name '*.pl' -o -name '*.pm' \) | sed 's@^\./@@'
+  fi
+} | xargs -n 1 perl -c -Itests