Add a script to generate a stub libcurl library

Linking to this library will make DDNet compatible with all distros that
ship libcurl.so.4 with arbitrary version data attached. Distros
sometimes add versioning information to the symbols exported by curl
that artificially (because they're compatible with each other) limit
where our releases can be executed if dynamically linked.

This should reduce release size a bit and let's us take advantage of
automatically updated libraries.

scripts/generate_fake_curl.py

@@ -0,0 +1,74 @@
+#!/usr/bin/env python3
+import argparse
+import os
+import re
+import subprocess
+import tempfile
+
+os.chdir(os.path.dirname(__file__) + "/..")
+PATH = "src/"
+
+
+CURL_RE=re.compile(r"\bcurl_\w*")
+
+def get_curl_calls(path):
+	names = set()
+	for dir, _, files in os.walk(path):
+		for filename in files:
+			if (filename.endswith(".cpp") or
+					filename.endswith(".c") or
+					filename.endswith(".h")):
+				with open(os.path.join(dir, filename)) as f:
+					contents = f.read()
+				names = names.union(CURL_RE.findall(contents))
+	return names
+
+def assembly_source(names):
+	names = sorted(names)
+	result = []
+	for name in names:
+		result.append(".type {},@function".format(name))
+	for name in names:
+		result.append(".global {}".format(name))
+	for name in names:
+		result.append("{}:".format(name))
+	return "\n".join(result + [""])
+
+DEFAULT_OUTPUT="libcurl.so"
+DEFAULT_SONAME="libcurl.so.4"
+
+def main():
+	p = argparse.ArgumentParser(description="Create a stub shared object for linking")
+	p.add_argument("-k", "--keep", action="store_true", help="Keep the intermediary assembly file")
+	p.add_argument("--output", help="Output filename (default: {})".format(DEFAULT_OUTPUT), default=DEFAULT_OUTPUT)
+	p.add_argument("--soname", help="soname of the produced shared object (default: {})".format(DEFAULT_SONAME), default=DEFAULT_SONAME)
+	p.add_argument("--functions", metavar="FUNCTION", nargs="+", help="Function symbols that should be put into the shared object (default: look for curl_* names in the source code)")
+	p.add_argument("--link-args", help="Colon-separated list of additional linking arguments")
+	args = p.parse_args()
+
+	if args.functions is not None:
+		functions = args.functions
+	else:
+		functions = get_curl_calls(PATH)
+	extra_link_args = []
+	if args.link_args:
+		extra_link_args = args.link_args.split(":")
+
+	with tempfile.NamedTemporaryFile("w", suffix=".s", delete=not args.keep) as f:
+		if args.keep:
+			print("using {} as temporary file".format(f.name))
+		f.write(assembly_source(functions))
+		f.flush()
+		subprocess.check_call([
+			"cc",
+		] + extra_link_args + [
+			"-shared",
+			"-nostdlib", # don't need to link to libc
+			"-Wl,-soname,{}".format(args.soname),
+			"-o", args.output,
+			f.name,
+		])
+		subprocess.check_call(["strip", args.output])
+
+if __name__ == '__main__':
+	main()