Fix riscv64 fuchsia LLVM target name

Author: taiki-e

compiler/rustc_target/src/spec/riscv64gc_unknown_fuchsia.rs

@@ -2,7 +2,7 @@ use crate::spec::{CodeModel, SanitizerSet, Target, TargetOptions};
 
 pub fn target() -> Target {
     Target {
-        llvm_target: "riscv64gc-unknown-fuchsia".into(),
+        llvm_target: "riscv64-unknown-fuchsia".into(),
         pointer_width: 64,
         data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
         arch: "riscv64".into(),