Add riscv64gc-unknown-redox

Co-Authored-By: Jeremy Soller <jackpot51@gmail.com>

compiler/rustc_target/src/spec/mod.rs

@@ -1553,6 +1553,7 @@ supported_targets! {
 
     ("aarch64-unknown-redox", aarch64_unknown_redox),
     ("i586-unknown-redox", i586_unknown_redox),
+    ("riscv64gc-unknown-redox", riscv64gc_unknown_redox),
     ("x86_64-unknown-redox", x86_64_unknown_redox),
 
     ("x86_64-unknown-managarm-mlibc", x86_64_unknown_managarm_mlibc),

compiler/rustc_target/src/spec/targets/riscv64gc_unknown_redox.rs

@@ -0,0 +1,25 @@
+use crate::spec::{CodeModel, Target, TargetMetadata, base};
+
+pub(crate) fn target() -> Target {
+    let mut base = base::redox::opts();
+    base.code_model = Some(CodeModel::Medium);
+    base.cpu = "generic-rv64".into();
+    base.features = "+m,+a,+f,+d,+c".into();
+    base.llvm_abiname = "lp64d".into();
+    base.plt_by_default = false;
+    base.max_atomic_width = Some(64);
+
+    Target {
+        llvm_target: "riscv64-unknown-redox".into(),
+        metadata: TargetMetadata {
+            description: Some("Redox OS".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(true),
+        },
+        pointer_width: 64,
+        data_layout: "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128".into(),
+        arch: "riscv64".into(),
+        options: base,
+    }
+}