add riscv64gc-unknown-openbsd support (target riscv64-unknown-openbsd on OpenBSD)

- add platform-support documentation
- add riscv64gc-unknown-openbsd spec
- do not try to link with -latomic on openbsd

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/rustc_llvm/build.rs b/compiler/rustc_llvm/build.rs
index abb68f3afe5..28e092c1eb7 100644
--- a/compiler/rustc_llvm/build.rs
+++ b/compiler/rustc_llvm/build.rs
@@ -342,10 +342,10 @@ fn main() {
     };
 
     // RISC-V GCC erroneously requires libatomic for sub-word
-    // atomic operations. FreeBSD uses Clang as its system
+    // atomic operations. Some BSD uses Clang as its system
     // compiler and provides no libatomic in its base system so
     // does not want this.
-    if !target.contains("freebsd") && target.starts_with("riscv") {
+    if target.starts_with("riscv") && !target.contains("freebsd") && !target.contains("openbsd") {
         println!("cargo:rustc-link-lib=atomic");
     }