Tests for config.rpath and lib-link.m4.

rpath-1 w
        |
        +---- a = static, b = shared

rpath-2 u v w
        | | |
        | | +---- a = static/static, b = static/shared,
        | |       c = shared/static, d = shared/shared.
        | |
        | +------ a = all libraries and the program have the same prefix,
        |         b = the libraries are in different directories.
        |
        +-------- a = all shared libraries use the libtool *.la files for
                  resolving dependencies, b = dependencies are given as
                  AC_LIB_LINKFLAGS argument instead.

The rpath-2* tests are sensitive to
  - incomplete shared library support in the system,
  - bugs in libtool that creates the shared libraries,
  - bugs in lib-link.m4.

Known failures:

* OSF/1 4.0: rpath-2bbd fails, because -rpath options are not cumulative:
  The last -rpath option overrides all previous ones. One would need to
  pass all directories, separated by colons, in a single -rpath option.