Rollup merge of #50678 - semarie:openbsd-targets, r=sanxiyn

Update openbsd targets

- add a new target `aarch64-unknown-openbsd`
- update `i686-unknown-openbsd` to use lld with clang, in order to correctly link binaries with `i128`

src/librustc_target/spec/aarch64_unknown_openbsd.rs

+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use spec::{LinkerFlavor, Target, TargetResult};
+
+pub fn target() -> TargetResult {
+    let mut base = super::openbsd_base::opts();
+    base.max_atomic_width = Some(128);
+    base.abi_blacklist = super::arm_base::abi_blacklist();
+
+    Ok(Target {
+        llvm_target: "aarch64-unknown-openbsd".to_string(),
+        target_endian: "little".to_string(),
+        target_pointer_width: "64".to_string(),
+        target_c_int_width: "32".to_string(),
+        data_layout: "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".to_string(),
+        arch: "aarch64".to_string(),
+        target_os: "openbsd".to_string(),
+        target_env: "".to_string(),
+        target_vendor: "unknown".to_string(),
+        linker_flavor: LinkerFlavor::Gcc,
+        options: base,
+    })
+}

src/librustc_target/spec/i686_unknown_openbsd.rs

@@ -15,6 +15,7 @@ pub fn target() -> TargetResult {
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
+    base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-fuse-ld=lld".to_string());
     base.stack_probes = true;
 
     Ok(Target {

src/librustc_target/spec/mod.rs

@@ -313,6 +313,7 @@ fn $module() {
 
     ("x86_64-unknown-bitrig", x86_64_unknown_bitrig),
 
+    ("aarch64-unknown-openbsd", aarch64_unknown_openbsd),
     ("i686-unknown-openbsd", i686_unknown_openbsd),
     ("x86_64-unknown-openbsd", x86_64_unknown_openbsd),