[RISCV] Add testcase for return address signing for outlined functions

[hiraditya]

Adapted from: AArch64/machine-outliner-retaddr-sign-non-leaf.ll

Towards: #114437

[ilovepi]

Does RISC-V support return address signing? I don't recall a ratified extension that does that.

Additionally, the test code uses X30 as the return reg, which seems like a mistranslation from Aarch64. I also see that the test uses auti{a,b}sp, which are Aarch64 instructions, right? I think they only pass FileCheck because those instructions don't exist for rv64, and they're used in a CHECK-NOT: directive.

Given that we're not testing the signing, and the test IR doesn't seem materially different from the existing cases, do we need this test?

[hiraditya]

Does RISC-V support return address signing? I don't recall a ratified extension that does that.

Additionally, the test code uses X30 as the return reg, which seems like a mistranslation from Aarch64. I also see that the test uses auti{a,b}sp, which are Aarch64 instructions, right? I think they only pass FileCheck because those instructions don't exist for rv64, and they're used in a CHECK-NOT: directive.

Given that we're not testing the signing, and the test IR doesn't seem materially different from the existing cases, do we need this test?

yeah i'll just abandon this.