[llvm-branch-commits] [RISCV] Select the capability ABI by default when the Y extension is enabled (PR #213411)

[Alexander Richardson via llvm-branch-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/213411

computeDefaultABI() previously had no knowledge of the Y (CHERI)
extension, so a target with Y enabled and no explicit -target-abi
would fall back to the plain integer ABI instead of il32pc64(d)/
l64pc128(d).

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