libbsd include path issue

[Christian Mauderer]

Hello Sichen,

as discussed in our private chat I'm quite convinced that your problem
is that the source file is in "freebsd/crypto/openssl/crypto" which
doesn't end on a path called "openssl".

As far as I can see, there is currently no support in our build system
for such cases. I created a (still quite uggly) hack that tries to copy
the headers to a path in the build tree. Could you please try out the
(mostly untested) attached patch? You should be able to specify
headerPaths() lines in builder.py which have different endings than the
original source paths.

To our waf experts: Please tell me, that there is a better solution. If
not, it would be good if you could give me some feedback for a better
and cleaner solution. And: I currently only tried half a build. Do you
see any problems on any platforms on build or install with that
solution?

Kind regards

Christian