Simplify compiler calling convention handling

Matcher::calling_convention/c_calling_convention simply delegate to SharedRuntime::java_calling_convention/c_calling_convention on all platforms. Since the SPARC removal the is_outgoing argument is also never used, neither in these nor in the return_value methods.

I think we can refactor this and move some related methods out from the .ad files.

This might have a tiny positive impact by reducing calls and improving inlining (at least gcc has a hard time inlining anything that goes in the .ad files, even when it's defined to the same class), but is mainly a cleanup effort.