Add riscv64gc-unknown-freebsd

compiler/rustc_llvm/build.rs

@@ -277,7 +277,7 @@ fn main() {
     };
 
     // RISC-V requires libatomic for sub-word atomic operations
-    if target.starts_with("riscv") {
+    if !target.contains("freebsd") && target.starts_with("riscv") {
         println!("cargo:rustc-link-lib=atomic");
     }
 

compiler/rustc_target/src/spec/mod.rs

@@ -813,6 +813,7 @@ supported_targets! {
     ("powerpc-unknown-freebsd", powerpc_unknown_freebsd),
     ("powerpc64-unknown-freebsd", powerpc64_unknown_freebsd),
     ("powerpc64le-unknown-freebsd", powerpc64le_unknown_freebsd),
+    ("riscv64gc-unknown-freebsd", riscv64gc_unknown_freebsd),
     ("x86_64-unknown-freebsd", x86_64_unknown_freebsd),
 
     ("x86_64-unknown-dragonfly", x86_64_unknown_dragonfly),

compiler/rustc_target/src/spec/riscv64gc_unknown_freebsd.rs

@@ -0,0 +1,18 @@
+use crate::spec::{CodeModel, Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "riscv64-unknown-freebsd".to_string(),
+        pointer_width: 64,
+        data_layout: "e-m:e-p:64:64-i64:64-i128:128-n64-S128".to_string(),
+        arch: "riscv64".to_string(),
+        options: TargetOptions {
+            code_model: Some(CodeModel::Medium),
+            cpu: "generic-rv64".to_string(),
+            features: "+m,+a,+f,+d,+c".to_string(),
+            llvm_abiname: "lp64d".to_string(),
+            max_atomic_width: Some(64),
+            ..super::freebsd_base::opts()
+        },
+    }
+}