For arch variants loongson and r1 neg instruction does not change the
sign for NaN-like operands, the same as r2 neg. This fix adjusts macro
assembler Neg_s and Neg_d arch variant logic so the correct code would
be generated for loongson and r1.

BUG=

Review-Url: https://codereview.chromium.org/2287333002
Cr-Commit-Position: refs/heads/master@{#39007}