Fix cross compiling to aarch64 macOS

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Fix incorrect platform detection for Windows in `pyo3-build-config`. [#2198](https://github.com/PyO3/pyo3/pull/2198)
+- Fix cross compiling to aarch64 macOS. [#2201](https://github.com/PyO3/pyo3/pull/2201)
 
 ## [0.16.0] - 2022-02-27
 

pyo3-build-config/src/impl_.rs

@@ -623,7 +623,16 @@ pub fn cross_compiling(
     let cross_lib_dir = env_var("PYO3_CROSS_LIB_DIR");
     let cross_python_version = env_var("PYO3_CROSS_PYTHON_VERSION");
 
-    let target_triple = format!("{}-{}-{}", target_arch, target_vendor, target_os);
+    let target_triple = format!(
+        "{}-{}-{}",
+        target_arch,
+        target_vendor,
+        if target_os == "macos" {
+            "darwin"
+        } else {
+            target_os
+        }
+    );
 
     if cross.is_none() && cross_lib_dir.is_none() && cross_python_version.is_none() {
         // No cross-compiling environment variables set; try to determine if this is a known case