protobuf-c does not compile on Solaris 10, as bind/connect/etc. are in libsocket

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What steps will reproduce the problem?
1. build protobuf-c on Solaris

What is the expected output? What do you see instead?
I expect it to build; it does not build

What version of the product are you using? On what operating system?
0.15 on Solaris

Please provide any additional information below.
Here's a trivial patch for the autotools build system that will check for bind 
first without libs, and then with libsocket. The -lnsl at the end is also 
required for Solaris 10.

I would've replicated this in CMake, however no part of that build system works 
under Solaris, so I didn't even bother.

https://codereview.appspot.com/14001043

Original issue reported on code.google.com by ay1244 on 26 Sep 2013 at 11:17