Add loongarch support and LSX SIMD optimizations

[XiWeiGu]

Enable LSX by default: ./autogen.sh --maintainer && ./configure && make
Disable LSX: ./autogen.sh --maintainer && ./configure --enable-loongarch-lsx=no && make

[XiWeiGu]

@ctruta , Could you please take some time to review the code?

[ctruta]

Looks good to me.

[ctruta]

Oops I almost missed one thing: that the libpng developers (not the users) are the ones who run
./autogen.sh --maintainer
I'll do this for you.

[ctruta]

Done. See a7fe341.

... but now, after landing the last three commits, ./configure --enable-hardware-optimizations is broken, and we must have it fixed before we ship the next release. Could you please take a look?

While at it, could you also verify if I updated the AUTHORS file correctly?

[XiWeiGu]

I will address it promptly.

[ctruta]

Thank you. Could you please also have a look at compilation with
gcc -Wundef
because that one is complaining as well.

[XiWeiGu]

Done. See a7fe341.

... but now, after landing the last three commits, ./configure --enable-hardware-optimizations is broken, and we must have it fixed before we ship the next release. Could you please take a look?

I apologize for the oversight and appreciate your reminder. The issue has been addressed in the PR #526

[XiWeiGu]

While at it, could you also verify if I updated the AUTHORS file correctly?

"ZhangLixia" has resigned and is no longer maintaining the Loongson ecosystem. I suggest replacing her with "JinBo," who is the primary contributor to LoongArch LSX optimizations.

[XiWeiGu]

Thank you. Could you please also have a look at compilation with gcc -Wundef because that one is complaining as well.

Reiterating my gratitude. PR #527 has already fixed this issue.

[ctruta]

While at it, could you also verify if I updated the AUTHORS file correctly?

"ZhangLixia" has resigned and is no longer maintaining the Loongson ecosystem. I suggest replacing her with "JinBo," who is the primary contributor to LoongArch LSX optimizations.

This is very good to know, thanks. I added JinBo to the list of authors.

About ZhangLixia, I'm still keeping her name in there, because she co-authored source code such as mips/filter_mmi_inline_assembly.c, in official Loongson capacity, and that merit is not going to "expire" 🙂

And, if I may please ask for yet one more favour. The Authors file is in ASCII right now, but I want to convert it to UTF-8 eventually. Could you please send me the correct Chinese spellings for all Loongson contributors?

[jinboson]

Could you please send me the correct Chinese spellings for all Loongson contributors?

GuXiWei --> 顾希伟
JinBo --> 金波
ZhangLixia --> 张利霞

Hope this may help. Thx!