Add initial LoongArch64 CPU support

[liushuyu]

This pull request ports the D runtime to LoongArch64 CPU architecture.

LoongArch64 is a new CPU architecture and has been supported by GCC (since GCC 13) and LLVM/Clang (since LLVM 16).

You can find more information about this architecture here: https://loongson.github.io/LoongArch-Documentation/README-EN.html

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Testing this PR locally

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[liushuyu]

Cross-reference:

• LDC: Add initial support for LoongArch64 ldc-developers/ldc#4500
• GDC: https://gcc.gnu.org/pipermail/gcc-patches/2023-September/631241.html https://gcc.gnu.org/pipermail/gcc-patches/2023-September/631260.html

[WalterBright]

I'm puzzled. There's LoongArch64, LoongArch32, LoongArch_HardFloat, and LoongArch_SoftFloat. But the only one that is used is LoongArch64. I suggest not defining the others until there's a use case (otherwise we could define all kinds of architectures that we don't support, which is pointless).

[WalterBright]

Other than that, I approve this.

[xen0n]

Yeah currently Linux only supports the 64-bit userland, and 32-bit LoongArch support is patchy right now. I'd agree with only defining LoongArch64 (and maybe the hard-float symbol) until use cases for the rest arise.

[ibuclaw]

Something should perhaps be predefined though when the base architecture is !TARGET_64BIT in gdc/ldc backend, otherwise there is no indication that compiler is generating code for a LoongArch processor.

[liushuyu]

Something should perhaps be predefined though when the base architecture is !TARGET_64BIT in gdc/ldc backend, otherwise there is no indication that compiler is generating code for a LoongArch processor.

I agree with that. Currently, GDC and LDC implementations for LoongArch32/64 architectures do use all those version identifiers.

[liushuyu]

I have rebased this pull request against the latest master branch.

[liushuyu]

Hi,

What is the status of this pull request? Should I do something or tag someone for review?