Improve avoiding C++ linkage, definition creation and cmake tests (#710)

src/gen-def.py

diff --git a/src/gen-def.py b/src/gen-def.py
new file mode 100755
index 0000000..ad1606e
--- /dev/null
+++ b/src/gen-def.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python
+
+from __future__ import print_function
+
+import io, os, re, sys
+
+headers_content = []
+for h in os.environ["headers"].split (' '):
+	if h.endswith (".h"):
+		with io.open(h, encoding='utf8') as f: headers_content.append (f.read ())
+
+result = ("EXPORTS\n" +
+	"\n".join (sorted (re.findall (r"^hb_\w+(?= \()", "\n".join (headers_content), re.M))) +
+	"\nLIBRARY libharfbuzz-0.dll")
+
+with open (sys.argv[1], "w") as f: f.write (result)