build-aux: rewrite duplicate header checker in Python

As part of an goal to eliminate Perl from libvirt build tools,
rewrite the prohibit-duplicate-header.pl tool in Python.

This was a straight conversion, manually going line-by-line to
change the syntax from Perl to Python. Thus the overall structure
of the file and approach is the same.

Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

scripts/prohibit-duplicate-header.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2016-2019 Red Hat, Inc.
+#
+# This 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.
+#
+# This 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 this library.  If not, see
+# <http://www.gnu.org/licenses/>.
+
+from __future__ import print_function
+
+import re
+import sys
+
+
+def check_file(filename):
+    includes = {}
+    lineno = 0
+    errs = False
+    with open(filename, "r") as fh:
+        for line in fh:
+            lineno = lineno + 1
+
+            headermatch = re.search(r'''^# *include *[<"]([^>"]*\.h)[">]''', line)
+            if headermatch is not None:
+                inc = headermatch.group(1)
+
+                if inc in includes:
+                    print("%s:%d: %s" % (filename, lineno, inc),
+                          file=sys.stderr)
+                    errs = True
+                else:
+                    includes[inc] = True
+
+    return errs
+
+
+ret = 0
+
+for filename in sys.argv[1:]:
+    if check_file(filename):
+        ret = 1
+
+if ret == 1:
+    print("Do not include a header more than once per file", file=sys.stderr)
+
+sys.exit(ret)