libffi: set target triplet to aarch64-apple-darwin on Mac M1. (#23750)

var/spack/repos/builtin/packages/libffi/package.py

@@ -32,4 +32,9 @@ def configure_args(self):
             # Spack adds its own target flags, so tell libffi not to
             # second-guess us
             args.append('--without-gcc-arch')
+        # At the moment, build scripts accept 'aarch64-apple-darwin'
+        # but not 'arm64-apple-darwin'.
+        # See: https://github.com/libffi/libffi/issues/571
+        if self.spec.satisfies('platform=darwin target=aarch64:'):
+            args.append('--build=aarch64-apple-darwin')
         return args