Fix issue #232. Add an option to exclude certain arguments from being
passed to clang.

You can now put this into your ~/.rdmrc

--block-argument -mfoobar

And -mfoobar will be stripped out before being passed to clang.

If your arg takes a value you can do this:

--block-argument -mfoobar=

And your command line looks like this:

gcc-something -mfoobar 12 foo.c

Clang will only see gcc-something foo.c