[PATCH] Add two new calling conventions for runtime calls

[Juergen Ributzka]

Hi @ll,

this patch adds two new target-independent calling conventions for runtime calls - Runtime and FastRuntime.

The target-specific implementation for X86-64 is defined as following:
	- Arguments are passed as for the default C calling convention
	- The same applies for the return value(s)
	- for runtimecc the callee preserves all GPRs - except R11
	- for fastruntimecc the callee preserves all GPRs and all XMMs - except R11

The idea is to provide calling conventions for calls to very hot runtime functions that are normally just a few lines of assembly code and don’t require a lot of registers. This could be used by the ObjectiveC runtime, or any other runtime that provides performance critical functions.

The FastRuntime CC is intended to be used for small codes that don’t call any other functions at all.
The Runtime CC is also intended for small codes that usually don’t call other functions on the fast path, but might have to on the slow path.

Cheers,
Juergen

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