Solaris build fixes.
Solaris build fixes.

* SConstruct:
  (link_rpath): generate a platform-specific link flag for setting the
    RPATH in a library/executable.
  (linkflags): use link_rpath in both linkflags assignments
  (libs): add -lm for Solaris

jandre/serf,jandre/serf,jandre/serf,jandre/serf