Document check and distcheck make targets

Also synchronize ldconfig configuration documentation.
Test for cygwin to avoid Linux specific code

Compile failed on Cygwin looking for Linux specific header files.  Add a
preprocessor test for cygwin to only compile Windows compatible code.
Quell compiler warnings on Cygwin

Quell mostly harmless warnings from the older GCC installed in Cygwin.
Produces a quiet compilation.
Specify AC_CONFIG_LIBOBJ_DIR as lib

As AC_LIBOBJ is used, make sure that the lib directory is known to the
build system.
Specify libhamlib.la dependencies