[clang] [RISCV][clang] Don't enable -mrelax-all for -O0 on RISC-V (PR #88538)

[Fangrui Song via cfe-commits]

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@@ -1,4 +1,4 @@
-// XFAIL: target={{.*}}-aix{{.*}}
+// XFAIL: target={{.*}}-aix{{.*}}, target=riscv{{.*}}
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MaskRay wrote:

This causes different behaviors with the default target triple, which is probably not perfect.

I think we can change the -mrelax-all check with an explicit target triple and then add a `--target=riscv64`.

https://github.com/llvm/llvm-project/pull/88538