CI: fix linking in test build with Anaconda c++

For some reason Anaconda linker on Linux needs `-rpath-link` in addition
to `-rpath` to resolve secondary dependencies at link time.

Author: pavoljuhas

Diff for: .travis-sconscript.local

@@ -28,5 +28,7 @@ env.Prepend(CCFLAGS=['-isystem{}/include'.format(P)])
 L = P + '/lib'
 env.Append(LIBPATH=L)
 env.Append(LINKFLAGS='-Wl,-rpath,{!r}'.format(L))
+if env['PLATFORM'] == 'posix':
+    env.Append(LINKFLAGS='-Wl,-rpath-link,{!r}'.format(L))
 
 # vim: ft=python