Bug 1914947 - Build Intel mac clang on arm64 workers. r=firefox-build-system-reviewers,sergesanspaille

That's actually much faster.

Differential Revision: https://phabricator.services.mozilla.com/D220531

build/build-clang/build-clang.py

@@ -180,7 +180,16 @@ def is_windows(target):
 
 
 def is_cross_compile(target):
-    return SUPPORTED_TARGETS[target] != (platform.system(), platform.machine())
+    target_system, target_machine = SUPPORTED_TARGETS[target]
+    system, machine = (platform.system(), platform.machine())
+    if system != target_system:
+        return True
+    # Don't consider x86 mac on arm64 mac a cross-compile so that we
+    # can build x86 mac clang on arm64 mac via Rosetta, as if they
+    # were building on x86.
+    if system == "Darwin" and machine == "arm64":
+        return False
+    return machine != target_machine
 
 
 def build_one_stage(