Rollup merge of rust-lang#138427 - madsmtm:vxworks-llvm-target, r=jieyouxu

Fix RISC-V VxWorks LLVM target triples

The targets `riscv32-wrs-vxworks` and `riscv64-wrs-vxworks` uses the plain `$ARCH` LLVM triple, which LLVM normalizes to `$ARCH-unknown-unknown`, we should use `$ARCH-unknown-linux-gnu$ABI` which is consistent with the the other VxWorks targets.

Motivation: To make it easier to verify that [`cc-rs`' conversion from `rustc` to Clang/LLVM triples](rust-lang/cc-rs#1431) is correct.

Alternative: Pass `$ARCH-unknown-none` in the other VxWorks LLVM triples, I don't know anything about VxWorks, so am unsure which is the most correct option.

CC target maintainer `@biabbas.`
r? jieyouxu

Author: matthiaskrgr

compiler/rustc_target/src/spec/targets/riscv32_wrs_vxworks.rs

@@ -2,7 +2,7 @@ use crate::spec::{StackProbeType, Target, TargetMetadata, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
-        llvm_target: "riscv32".into(),
+        llvm_target: "riscv32-unknown-linux-gnu".into(),
         metadata: TargetMetadata {
             description: None,
             tier: Some(3),

compiler/rustc_target/src/spec/targets/riscv64_wrs_vxworks.rs

@@ -2,7 +2,7 @@ use crate::spec::{StackProbeType, Target, TargetMetadata, TargetOptions, base};
 
 pub(crate) fn target() -> Target {
     Target {
-        llvm_target: "riscv64".into(),
+        llvm_target: "riscv64-unknown-linux-gnu".into(),
         metadata: TargetMetadata {
             description: None,
             tier: Some(3),