cmd/compile/internal/ssa: add codegen for Zicond extension on riscv64

[lxq015]

This patch adds code generation support for the Zicond extension.

We convert branches into CondSelect operations in branchelim and rewrite them into Zicond instructions. Additionally, optimization rules have been added to optimize more conditional branch scenarios based on the riscv-isa-manual.

Follow-up to CL 631595
Updates #75350

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Mark Ryan:

Patch Set 1:

(1 comment)

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[gopherbot]

This PR (HEAD: 58e1e0c) has been imported to Gerrit for code review.

Please visit Gerrit at https://go-review.googlesource.com/c/go/+/705996.

Important tips:

• Don't comment on this PR. All discussion takes place in Gerrit.
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• To change your code in response to feedback:
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  • Edit these as needed via the GitHub web interface (not via Gerrit or git).
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[gopherbot]

Message from Xueqi Luo:

Patch Set 2:

(2 comments)

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