Revert "Revert "Support unresolved fields in optimizing"

The CL also changes the calling convetion for 64bit static field set
to use kArg2 instead of kArg1. This allows optimizing to keep
the asumptions:
- arm pairs are always of form (even_reg, odd_reg)
- ecx_edx is not used as a register on x86.

This reverts commit e6f49b47.

Change-Id: I93159917565824084abc96775f31be1a4249f2f3