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 e6f49b47b6a4dc9c7684e4483757872cfc7ff1a1.

Change-Id: I93159917565824084abc96775f31be1a4249f2f3
diff --git a/runtime/arch/mips64/quick_entrypoints_mips64.S b/runtime/arch/mips64/quick_entrypoints_mips64.S
index ce1b2f3..68156ae 100644
--- a/runtime/arch/mips64/quick_entrypoints_mips64.S
+++ b/runtime/arch/mips64/quick_entrypoints_mips64.S
@@ -1244,7 +1244,7 @@
     .extern artSet64StaticFromCode
 ENTRY art_quick_set64_static
     SETUP_REFS_ONLY_CALLEE_SAVE_FRAME    # save callee saves in case of GC
-    move   $a2, $a1                      # pass new_val
+                                         # a2 contains the new val
     ld     $a1, FRAME_SIZE_REFS_ONLY_CALLEE_SAVE($sp)  # pass referrer's Method*
     jal    artSet64StaticFromCode        # (field_idx, referrer, new_val, Thread*)
     move   $a3, rSELF                    # pass Thread::Current