Suggestion to rename mingw's i386 target to i686 for Xmake 3

[ifarbod]

Xmake 3 introduces breaking changes, right?

So why not rename the MinGW target to i686 as it's exclusively known as that? And maybe provide a backup option for people who still use i386.

Some references:

https://github.com/msys2/MSYS2-packages/blob/ecb03e70dc7ac85e2d2fffa015e4fbfd3308d378/fish/msystem.fish#L19

https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/MinGW.cpp#L648

https://github.com/JuliaLang/julia/blob/master/test/binaryplatforms.jl#L171

[waruqi]

You can mention it at #5527

[waruqi]

#5906

[jingkaimori]

usage of i386 for mingw plat:

• https://github.com/ssbssa/gdb/blob/22b96f176da2e42a73bb665c5578be3d98c9de43/gas/NEWS#L350

[TurnOffNOD]

i686 means that compiled binary should run at least 686 architecture, and means it drops out suport of architecture older than 686.

i386 means that it still supports architecture older than 686.

[waruqi]

I added a poll option, x86_64, i386, i686

#5906