Cleaned up the ABI::PrepareTrivialCall() function to take three argument

pointers:

        virtual bool
        PrepareTrivialCall (Thread &thread, 
                            lldb::addr_t sp,
                            lldb::addr_t functionAddress,
                            lldb::addr_t returnAddress, 
                            lldb::addr_t *arg1_ptr,
                            lldb::addr_t *arg2_ptr,
                            lldb::addr_t *arg3_ptr) const = 0;

Prior to this it was:

        virtual bool
        PrepareTrivialCall (Thread &thread, 
                            lldb::addr_t sp,
                            lldb::addr_t functionAddress,
                            lldb::addr_t returnAddress, 
                            lldb::addr_t arg,
                            lldb::addr_t *this_arg,
                            lldb::addr_t *cmd_arg) const = 0;

This was because the function that called this slowly added more features to
be able to call a C++ member function that might have a "this" pointer, and 
then later added "self + cmd" support for objective C. Cleaning this code up
and the code that calls it makes it easier to implement the functions for
new targets.

The MacOSX_arm::PrepareTrivialCall() is now filled in and ready for testing.

llvm-svn: 131221