feat: add gomips support

[xrz-cloud]

Add GOMIPS support when building for mips devices(like some openwrt routers).
GOMIPS can be set to hardfloat(default) or softfloat.

[wangyoucao577]

Thanks very much! wangyoucao577/[email protected] now ready for you.

[lslqtz]

Nice work, but I want to point out that GOMIPS may not work with mips64 and mips64le.

Ref: https://pkg.go.dev/cmd/[email protected]

For GOARCH=mips or mipsle, GOMIPS=hardfloat and softfloat correspond to the mips.hardfloat and mips.softfloat (or mipsle.hardfloat and mipsle.softfloat) feature build tags.
For GOARCH=mips64 or mips64le, GOMIPS64=hardfloat and softfloat correspond to the mips64.hardfloat and mips64.softfloat (or mips64le.hardfloat and mips64le.softfloat) feature build tags.