Whitelist supported link flags

Only keep known linker flags when parsing arguments. This avoids issues when passing linker flags with options like:

``-Wl,-rpath,/bin:/lib``

Which is turned into two arguments `-rpath` and `/bin:/lib` when passed to link(), the second of which is incorrectly interpreted as a file input (since it doesn't know about rpath).

This code will need to change if we need to support linker flags with options in the future, but I guess we'll cross that bridge when we get to it.