title: clang: warning: using sysroot for 'iPhoneSimulator' but targeting 'MacOSX' [-Wincompatible-sysroot]
body: <p>I am getting the following errors when I try to start react-native</p>
  <pre><code>gis00109@GIS00109 ~ % npx react-native start     
  clang: warning: using sysroot for 'iPhoneSimulator' but targeting 'MacOSX' [-Wincompatible-sysroot]
  ld: warning: building for macOS, but linking in .tbd file (/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator13.5.sdk/usr/lib/libc++.tbd) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator13.5.sdk/usr/lib/libSystem.tbd) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libcache.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libcommonCrypto.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libcompiler_rt.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libcopyfile.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libcorecrypto.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libdispatch.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libdyld.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/liblaunch.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libmacho.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libremovefile.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_asl.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_blocks.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_c.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_configuration.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_containermanager.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_coreservices.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_darwin.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_dnssd.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_featureflags.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_info.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_m.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_malloc.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_notify.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sandbox.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sim_kernel.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sim_platform.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sim_pthread.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_trace.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libunwind.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libxpc.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator13.5.sdk/usr/lib/libc++abi.tbd) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sim_kernel_host.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sim_platform_host.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_sim_pthread_host.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_kernel.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_platform.dylib) built for iOS Simulator
  ld: warning: building for macOS, but linking in .tbd file (/usr/lib/system/libsystem_pthread.dylib) built for iOS Simulator
  clang: warning: using sysroot for 'iPhoneSimulator' but targeting 'MacOSX' [-Wincompatible-sysroot]
  In file included from ../fsevents.cc:72:
  ../src/thread.cc:36:25: error: unknown type name 'ConstFSEventStreamRef'
  void HandleStreamEvents(ConstFSEventStreamRef stream, void *ctx, size_t ...
                          ^
  ../src/thread.cc:36:108: error: unknown type name 'FSEventStreamEventFlags'
    ...stream, void *ctx, size_t numEvents, void *eventPaths, const FSEventStre...
                                                                    ^
  ../src/thread.cc:36:152: error: unknown type name 'FSEventStreamEventId'
    ...*eventPaths, const FSEventStreamEventFlags eventFlags[], const FSEventSt...
                                                                      ^
  ../src/thread.cc:54:3: error: unknown type name 'FSEventStreamContext'
    FSEventStreamContext context = { 0, ctx, NULL, NULL, NULL };
    ^
  ../src/thread.cc:56:3: error: unknown type name 'FSEventStreamRef'
    FSEventStreamRef stream = FSEventStreamCreate(NULL, &amp;HandleStreamEvent...
    ^
  ../src/thread.cc:56:98: error: use of undeclared identifier
        'kFSEventStreamEventIdSinceNow'
    ...&amp;HandleStreamEvents, &amp;context, fse-&gt;paths, kFSEventStreamEventIdSinceNow...
                                                  ^
  6 errors generated.
  make: *** [Release/obj.target/fse/fsevents.o] Error 1
  gyp ERR! build error 
  gyp ERR! stack Error: `make` failed with exit code: 2
  gyp ERR! stack     at ChildProcess.onExit (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/build.js:194:23)
  gyp ERR! stack     at ChildProcess.emit (events.js:210:5)
  gyp ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:272:12)
  gyp ERR! System Darwin 19.5.0
  gyp ERR! command &quot;/usr/local/bin/node&quot; &quot;/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js&quot; &quot;rebuild&quot;
  gyp ERR! cwd /Users/gis00109/.npm/_npx/31282/lib/node_modules/react-native/node_modules/fsevents
  gyp ERR! node -v v12.13.1
  gyp ERR! node-gyp -v v5.1.0
  gyp ERR! not ok 
  </code></pre>