fuse4x-kext: Explicitly list architectures

Build `i386` for Leopard and a fat binary for everything else. Failing to be
explicit can cause `xcodebuild` to attempt building for more architectures than
it really should.

Fixes Homebrew#7619.

Library/Formula/fuse4x-kext.rb

@@ -19,10 +19,11 @@ def install
       "-configuration", "Release",
       "-alltargets",
       "MACOSX_DEPLOYMENT_TARGET=#{MACOS_VERSION}",
-      "SYMROOT=build"
+      "SYMROOT=build",
+      # Build a 32-bit kernel extension on Leopard and a fat binary for Snow
+      # Leopard/Lion.
+      "ARCHS=i386 #{'x86_64' unless MacOS.leopard?}", 'ONLY_ACTIVE_ARCH=NO'
     ]
-    # Don't build a multi-arch kext for Leopard---it will fail.
-    args.concat %w[ARCHS=i386 ONLY_ACTIVE_ARCH=NO] if MacOS.leopard?
 
     system "/usr/bin/xcodebuild", *args
     system "/bin/mkdir -p build/Release/fuse4x.kext/Support"