Issue #12326: don't test the major version of sys.platform

Use startswith, instead of ==, when testing sys.platform to support
new platforms like Linux 3 or OpenBSD 5.

setup.py

@@ -1381,9 +1381,8 @@ class PyBuildExt(build_ext):
         # End multiprocessing
 
         # Platform-specific libraries
-        if (platform in ('linux2', 'freebsd4', 'freebsd5', 'freebsd6',
-                        'freebsd7', 'freebsd8')
-            or platform.startswith("gnukfreebsd")):
+        if any(platform.startswith(prefix)
+               for prefix in ("linux", "freebsd", "gnukfreebsd")):
             exts.append( Extension('ossaudiodev', ['ossaudiodev.c']) )
         else:
             missing.append('ossaudiodev')