Same host_os normalisation as source3/wscript, so the winbind NSS
plugin is built on MidnightBSD.

--- nsswitch/wscript_build.orig
+++ nsswitch/wscript_build
@@ -2,6 +2,10 @@
 from waflib import Utils
 import sys
 host_os = sys.platform
+# MidnightBSD is FreeBSD-derived, but sys.platform reports midnightbsdN,
+# which none of the freebsd tests below match. Normalise it so they do.
+if host_os.rfind('midnightbsd') > -1:
+    host_os = host_os.replace('midnightbsd', 'freebsd')
 
 bld.SAMBA_BINARY('nsstest',
 		 source='nsstest.c',
