MFC r311174:

Make /usr/lib/libbsnmptools.so.0 into an INTERRNALLIB

Although it increases the size of the bsnmp{get,set,walk} binaries by
four on my [amd64] system, it removes the need for producing .debug
files, profiled libraries, and for installing the library itself,
reducing the overall size use on disk by the utilities noted
previously.

Plus, it guards against ABI/API compatibility issues with the library
as it's only used internal to the tools themselves.