OK, but the reason that we are getting the warnings is that none of the '**/Makefile*' files have the -isystem flag. I have tested the compilation and install using ````brew install ./subversion.rb --perl --ruby --with-python````, and all three swig flavours installed OK. I don't know how to test the ruby or python interfaces, so cannot verify that they work, but they did compile.

While testing, I noticed that the swig dependency had python in twice, and ruby not at all, so also fixed that.

Please let me know if you still want the this commit reverted, and I will do so.