Skip rustc version detection on macOS

src/bootstrap/bootstrap.py

@@ -209,6 +209,11 @@ def default_build_triple(verbose):
     # install, use their preference. This fixes most issues with Windows builds
     # being detected as GNU instead of MSVC.
     default_encoding = sys.getdefaultencoding()
+
+    if sys.platform == 'darwin':
+        print("not using rustc detection as it is unreliable on macOS")
+        print("falling back to auto-detect")
+    else:
         try:
             version = subprocess.check_output(["rustc", "--version", "--verbose"],
                     stderr=subprocess.DEVNULL)