More MIPS fixes. Many run-test tests pass.

Run-test tests 001-043 work, including 003-omnibus-opcodes. 044 is
proxy, which is still broken.

Changes made:
- Fixed argument marshalling of FP values for calls to helper functions
  in the compiler.
- Fixed CheckCast compilation's mistaken use of rARG0 instead of rRET0.
- Fixed conversion calls to marshall FP arguments properly.
- Created named values for FP args, though they differ in MIPS only.
- Fixed assembly to always use T9 to hold code pointer to jump to.
- Fixed proxy offset values.

Change-Id: If121db322683a307e5a1016210f4f73283aa817c