If it helps, profiling the hung process shows it's waiting for a synchronus reply. This machine is in an isolated network, and has no internet access. Call graph: 2449 Thread_20227 DispatchQueue_1: com.apple.main-thread (serial) + 2449 start (in dyld) + 462 [0x10e34e51e] + 2449 XcodeBuildMain (in libxcodebuildLoader.dylib) + 1286 [0x10a14d5d5] + 2449 -[Xcode3CommandLineBuildTool run] (in Xcode3Core) + 1814 [0x10a449e55] + 2449 LSRegisterURL (in LaunchServices) + 61 [0x7ff801990dbc] + 2449 _LSRegisterBundleURL (in LaunchServices) + 133 [0x7ff8019f5e0d] + 2449 _LSRegisterBundleNode (in LaunchServices) + 68 [0x7ff8019f5ea3] + 2449 LaunchServices::Database::Context::_get(unsigned int const*, unsigned long) (in LaunchServices) + 86 [0x7ff801a01e26] + 2449 _LSContextInitCommon(LSContext*, unsigned int const*, unsigned long, NSError* __autoreleasing*) (in LaunchServices) + 546 [0x7ff8019550d7] + 2449 _LSCopyServerStore (in LaunchServices) + 819 [0x7ff801895f34] + 2449 _NSXPCDistantObjectSimpleMessageSend1 (in Foundation) + 56 [0x7ff8022187b5] + 2449 -[NSXPCConnection _sendSelector:withProxy:arg1:] (in Foundation) + 119 [0x7ff80221887f] + 2449 -[NSXPCConnection _sendInvocation:orArguments:count:methodSignature:selector:withProxy:] (in Foundation) + 3163 [0x7ff802210f56] + 2449 __NSXPCCONNECTION_IS_WAITING_FOR_A_SYNCHRONOUS_REPLY__ (in Foundation) + 9 [0x7ff802212f16] + 2449 xpc_connection_send_message_with_reply_sync (in libxpc.dylib) + 238 [0x7ff801074dc4] + 2449 dispatch_mach_send_with_result_and_wait_for_reply (in libdispatch.dylib) + 50 [0x7ff80119813e] + 2449 _dispatch_mach_send_and_wait_for_reply (in libdispatch.dylib) + 514 [0x7ff801197d41] + 2449 mach_msg (in libsystem_kernel.dylib) + 56 [0x7ff8012fece8] + 2449 mach_msg_trap (in libsystem_kernel.dylib) + 10 [0x7ff8012fe97a] 2449 Thread_20228 2449 start_wqthread (in libsystem_pthread.dylib) + 15 [0x7ff801336f57] 2449 _pthread_wqthread (in libsystem_pthread.dylib) + 426 [0x7ff801338034] 2449 __workq_kernreturn (in libsystem_kernel.dylib) + 10 [0x7ff80130005a] code-block

Done. Bug FB15271895.