Remove an option not supported by clang.

I'm not certain when, if ever, clang supported the flag. Certainly in 3.5 it produces a fairly ugly warning:

    clang: warning: optimization flag '-finline-functions' is not supported
    clang: warning: argument unused during compilation: '-finline-functions'

The 3.5 release notes state that clang is now warning about options it doesn't understand -- previously it was silently ignoring them. I think it might be better to just turn it off for 3.5 and later, but I only know how to do this for specific versions, not a condition like < 3.5.