manual: support loong64

[D3Hunter]

Support build on loong64.
loong64 or Loongson (龙芯) is the name of a family of general-purpose, MIPS
architecture-compatible, later in-house LoongArch architecture microprocessors

[cockroach-teamcity]

This change is 

[D3Hunter]

@jbowens @RaduBerinde could you help review this? or give some feedback on how to contribute to this repo.

[RaduBerinde]

Thanks! Normally I'd say to fix it on master and then backport to release-1.1 and release-2.0. But this is no longer needed on master (as of #4227). I will merge this, can you open the same PR against release-2.0?

[RaduBerinde]

Can you give your comment a decent description? E.g. manual: support loong64

[D3Hunter]

comment changed, just found out that 2.0 has been fixed by #3631

original description, with useful links

Loongson (simplified Chinese: 龙芯; traditional Chinese: 龍芯; pinyin: Lóngxīn; lit. 'Dragon Core') is the name of a family of general-purpose, MIPS architecture-compatible, later in-house LoongArch architecture microprocessors

[RaduBerinde]

The commit itself just says "change".

[D3Hunter]

The commit itself just says "change".

sorry, I get used to another paradigm that will squash my commits and use PR title as commit message. I amend the commit message, ptal