librustc_trans: add fp64 to mips features whitelist
librustc_trans: add fp64 to mips features whitelist

On 32-bit MIPS, enabling MSA requires also enabling the 64-bit FPU.

GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust,graydon/rust