Add support for NetBSD/aarch64-be (big-endian arm64).

compiler/rustc_target/src/spec/aarch64_be_unknown_netbsd.rs

@@ -0,0 +1,17 @@
+use crate::abi::Endian;
+use crate::spec::{Target, TargetOptions};
+
+pub fn target() -> Target {
+    Target {
+        llvm_target: "aarch64_be-unknown-netbsd".into(),
+        pointer_width: 64,
+        data_layout: "E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".into(),
+        arch: "aarch64".into(),
+        options: TargetOptions {
+            mcount: "__mcount".into(),
+            max_atomic_width: Some(128),
+            endian: Endian::Big,
+            ..super::netbsd_base::opts()
+        },
+    }
+}

compiler/rustc_target/src/spec/mod.rs

@@ -1100,6 +1100,7 @@ fn $module() {
     ("x86_64-unknown-openbsd", x86_64_unknown_openbsd),
 
     ("aarch64-unknown-netbsd", aarch64_unknown_netbsd),
+    ("aarch64_be-unknown-netbsd", aarch64_be_unknown_netbsd),
     ("armv6-unknown-netbsd-eabihf", armv6_unknown_netbsd_eabihf),
     ("armv7-unknown-netbsd-eabihf", armv7_unknown_netbsd_eabihf),
     ("i686-unknown-netbsd", i686_unknown_netbsd),

src/bootstrap/bootstrap.py

@@ -327,6 +327,7 @@ def default_build_triple(verbose):
     cputype_mapper = {
         'BePC': 'i686',
         'aarch64': 'aarch64',
+        'aarch64eb': 'aarch64',
         'amd64': 'x86_64',
         'arm64': 'aarch64',
         'i386': 'i686',